GST Computer Systems Limited
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1. This section defines the various forms which a source line can take A source line consists of between O and 132 characters excluding the line feed character Basically a source line consists of the following four fields label optional but depends on operation operation optional operand depends on operation comment optional A source line can be blank including consisting entirely of comment as defined above in which case it is ignored for all purposes other than those connected with output listings a blank line is assigned a line number is printed on the listing and its position may affect the operation of the title directive The Label Field A line contains a label field if it starts with one of the following sequences of tokens lt symbol gt lt white space gt lt symbol gt lt white space gt lt symbol gt i e a label starting in column l may be followed by lt white space gt or a colon but a label starting further along the line must be terminated by a colon Such a sequence at the start of a line is referred to elsewhere in this appendix as a lt label gt If a line contains a label and contains nothing after the label then the label is defined with the current value of the current location counter otherwise the meaning of the label depends on the operation field The Operation Field The operation field follows the optional label field and its syntax is lt white space gt lt sym2. reread the description of the instruction or directive involved 1D size not allowed on directive Most directives do not accept a size extension the only ones that do allow a size are DC DCB amp DS lE invalid size The size specified on the instruction or directive is not legal 1F size B illegal for Areg Byte operations on address registers are not allowed 20 label illegal on this directive Many directives eg INCLUDE SECTION LIST PAGE do not accept a label 21 too many errors If a line has more than ten errors or warnings only the first ten are printed followed by this message 22 invalid operand s for this instruction The operand s specified are not valid for the instruction Check the rules for the instruction you are using in a 68000 manual If one of the operands to the instruction is an effective address this error can mean that the actual adressing mode specified is not legal The assembler will try to point the error flag the vertical bar character at the invalid operand but as the assembler may not even know in the case of a generic mnemonic which instruction you meant it will get this wrong sometimes 68K ASM User Manual 41 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler 23 undefined symbol The symbol has not been defined in the assembly 2h forward reference not allowed here Many directives do not allow a forward reference 25 short branch o
3. terminates completely This means for example that if you do a very large assembly followed by a very small assembly there will be no more free memory in the machine during the small assembly than there was during the large assembly Source Listing An optional source listing will be generated showing the source input and the code that has been generated The listings provided are controlled both by options on the command line see section 2 above and by directives coded in the source program see appendix B below If the NOLIST option is given then there will be ro listing output from the assembler Under all other circumstances a file or device will be used to produce a listing If the filename for the listing output is generated automatically by the assembler it will end in LIST It is recommended that listing files always have filenames ending in LIST but this is not a requirement and you can call them anything you like Listings can be printed directly as they are generated using TX1 or whatever is appropriate to your hardware and your implementation of 68K OS or can be sent to the screen using SCREEN as an elternative to sending them to files 68K ASM User Manual 10 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler 3 6 3 7 Symbol Table Listing A symbol table listing will be produced if both the LIST and SYM options are in effect The symbol table listing will be added to the end
4. To run the assembler a microdrive containing ASM PROG should be mounted and the program started by typing ASM PROG in ADAM s command line followed by ENTER If the microdrive cartridge has not been set as the program or data default directory you will need to precede the program name with a directory name see the 68K 0S User Manual If this file is present on the tape and provided no I O errors are detected the assembler will be loaded It will open large green window whose size car be adjusted using the grow and shrink functions and will output its rame revision rumber and a command line prompt Command Line Format The format of the command line is lt source gt lt listing gt lt binary gt lt option gt where lt option gt NOLIST ERRORS lt listing gt LIST lt listing gt NOBIN BIN lt binary gt NOSYM sym LIBRARY lt library gt LIB lt library gt the options may be in upper or lower case and case is not significant lt source gt lt file name gt file name of assembler source lt listing gt lt file name gt file name for listing output lt binary gt lt file name gt file name for binary output lt library gt lt file name gt file name for library input Command Line Options The options have the following meanings NOLIST de not generate any listing output ERRORS generate a listing of error messages and erroneous lines only if the option is followed
5. a few seconds Most 68K 08 errors relate to particular input or cutput files or devices and the file or device name involved is displayed as part of the message wherever possible In the case cf a serious error such as hard I O error affecting an input source file the assembler does not however tell you which of the various source e g INCLUDEd files is involved When an operating system error causes the assembler to terminate it returns the status code and any relevant file name to the calling program normally this is a command program which will probably display the messages again in case you weren t watching the assembler 68K ASM User Manual yh 8290 6 GST 68 1 03
6. absolute long lt expr gt PC relative lt expr gt PC PC relative lt expr gt PC lt ireg gt PC with index H lt expr gt immediate Note that the syntax lt expr gt means either PC with displacement addressing or either form of absolute addressing and this ambiguity is resolved according to the semantics of the lt expr gt See below for details Also the operand lt dreg gt e g could be either a register direct addressing mode or a lt multireg gt and hence a multiple register specification the assembler is capable of deciding what is meant depending on the instruction being assembled Interpretation of Addressing Modes Basically all references which involve relocatable destinations must be PC relative for the code to be position independent which is a requirement for running under 68K 0S This means that references to labels more than 32k bytes away will fail and the programmer must find some other means of reaching the destination All forms of the effective address are coded exactly as meant apart from lt expr gt which can mean en absolute short address an absolute long address or a PC relative address If the value of the lt expr gt is absolute the assembler will generate an absolute short address if possible otherwise it will generate an absolute long address 68K ASM User Manual 24 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler B 4 3 If the value of the lt expr gt is r
7. amp bitwise logical AND bitwise logical OR The order of evaluation of expressions is as follows a parenthesised expressions are evaluated first in the natural way b operators are evaluated according to priority the order of priority is highest first unary Cc binary c operators of the same precedence at the same nesting level of parentheses are evaluated from left to right Symbols may be absolute or relocatable Numbers and strings are absolute the current location counter is relocatable The oniy operators which may act on relocatable symbols or relocatable subexpressions are unary and and binary and When an expression has been fully evaluated it is one of a absolute the final value is independent of the start of section 0 b simple relocatable the final value is an cffset from the start of section O c complex relocatable the final value involves some other multiple of the start of section O 68K ASM User Manual 22 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler B 4 Addressing Modes This section defines all addressing modes that can be coded as instruction operands For a definition of what these addressing modes actually do consult a manual for the Motorola 68000 B h Addressing Mode Syntax A number of symbols are reserved and have special meaning when used in operands these are names of various registers DO to D7 data registers also
8. bytes of code then second listing line is used to display the rest of it this second listing line is blank apart from the generated code field and possibly some error flags Code in excess of 6 bytes generated by DC or DCB directives is not printed if you want to see it you should code several separate DC or DCB directives 68K ASM User Manual 13 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler The length of the listing line is in all cases limited to 132 characters any excess probably comment being truncated Error and warning messages are interspersed with the source listing each message follows the listing of the line to which it refers If a line has errors or warnings it is followed by a line containing a vertical bar character below the part cf the source line giving offence The format of the messages is k k ERROR xx line nnnn mmmm lt message gt WARNING xx line nnnn mmmm lt message gt where xx is the error number nnnn is the line number of the line containing the error mmmm is the line number of the line containing the previous error 0 if rone to allow the user to chain through all the error messages to make sure none have been missed and lt message gt is a helpful message saying what is wrong There are separate chains for error and warning messages The line giving rise to an error or warning is always listed regardless of the state of any LIST or NOLIST directive
9. not listed NOLIST Switch Listing Off The directive NOLIST suppresses listing until a LIST directive is encountered The NOLIST directive itself is not listed TITLE Define Title for Listing The directive TITLE lt title string gt causes the lt title string gt to be printed at the top of each subsequent page of listing If a title is wanted on the first page of the listing then the TITLE directive should appear before any source line which would get listed The TITLE directive itself is not listed 68K ASM User Manual 38 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler 68K ASM User Manual ERROR AND WARNING MESSAGES This appendix lists the error and warning messages which can be produced by the assembler in numerical order Error Messages 00 unknown instruction directive An unknown symbol has been rsed where an instruction or directive is expected in the operation field Ol illegal line after OFFSET Instructions and directives which generate code DC DCB are not allowed in the dummy section defined by the OFFSET directive Return to SECTION O before instructions or data 02 syntax error in instruction field The operation field does not contain a lt symbol gt 03 redefined symbol The symbol has already teen defined earlier in the assembly The first definition of the symbol will be used futher definitions will just produce this error message Ok phasing error T
10. the last two characters of the lt symbol gt depending on whether the operand length is byte word or long If a length is required and no length is coded the assembler will assume W and will print a warning message Instructions which may only take a single operand length may optionally have the length coded as above The branch instructions may optionally have S or L coded as the last two characters of the lt symbol gt to indicate the displacement size as described at B 4 3 above Examples MOVE L an instruction with an operand length coded BEQ S an instruction with an extent coded JSR an instruction with no extra bits MOVE L DO AO automatically generates MOVEA L MOVE L 2 D3 automatically generates MOVEQ L 68K ASM User Manual 26 8290 6 GST 68 1 03 er B 5 2 68K ASM Assembler Data Movement Instructions The various forms of the MOVE instruction are used to move data between registers and or memory These are MOVE lt length gt lt ea gt lt ea gt which is the generic instruction following if necessary and will generate one of the MOVEA lt length gt MOVEQ L lt ea gt lt areg gt i lt expr gt lt dreg gt Note that both MOVEA and MOVEQ can be coded explicitly if desired Note also that the assembler will only convert a MOVE to a MOVEQ if the length is specified as L Various other special forms of the MOVE instruction are always coded as MOVE they have no specific mnemonic but
11. the symbols DO W DO L etc AO to AY address registers also the symbols AO W AO L etc SP synonym for AT also the symbols SP W SP L USP user stack pointer CCR condition code register low 8 bits of SR SR status register PC program counter The syntax of instruction operands is developed below preceeded by a few general definitions lt areg gt AO AT SP lt dreg gt DO D7 lt ireg gt lt areg gt lt dreg gt AO W A7 W SP W DO W D7 W AO sus LATE SBE DO cvs DPE lt multireg gt lt range gt lt range gt lt range gt lt areg gt lt dreg gt lt areg gt lt areg gt lt dreg gt lt dreg gt where the registers in an individual range must be in increasing register order e g DO D3 is valid and Ak A is not valid 68K ASM User Manual 23 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler B 4 2 The addressing modes which are called by Motorola effective address and which can be coded or at least a subset of them in any instruction which has a general effective address as an operand are e lt ea gt lt dreg gt D register direct lt areg gt A register direct lt areg gt register indirect lt areg gt postincrement lt areg gt predecrement lt expr gt lt areg gt indirect with displacement lt expr gt lt areg gt lt ireg gt indirect with index lt expr gt absolute short lt expr gt
12. C directives 68K ASM User Manual 36 8290 6 GST 68 1 03 GST Computer Systems Limited K ASM Assembler B 6 8 B 6 9 B 6 10 DS Reserve Storage This cirective reserves memory locations The memory contents are undefined The directive is used to define offsets in conjunction with the OFFSET directive and to leave holes in data generated by DC and DCB it is also of use in ensuring that the current location counter has an even value Syntax lt label gt DS lt length gt lt expr gt If the length is W or L the current location counter whick can be a dummy location counter initiated by OFFSET is advanced to wore boundary if necessary The optional lt label gt is assigned the value of the adjusted location counter The lt expr gt must be absolute and contain no forward references DS B reserves lt expr gt bytes DS W reserves lt expr gt words and DS L reserves lt expr gt long words lt expr gt may have the value zero in which case DS W and DS L ensure that the location counter is on an even boundary and the optional lt label gt is defined DCB Define Constant Block The directive lt label gt DCB lt length gt lt expr gt lt expr gt causes the assembler to generate a block of bytes words or longs cepending on whether lt length gt is B W or L If the length is W or L the current location counter is advanced to a word boundary if necessary The optional lt labe
13. DE directive 68K ASM User Manual 8 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler 3 3 Library Input The assembler s library mechanism allows you to include in your program a previously assembled binary file containing useful subroutines or other code The program being assembled may refer to labels within the library but the library must be self contained and cannot refer to labels elsewhere in the program To use a library you must make reference to two files The first file is a set of symbol definitions in normal assembler source format which you must INCLUDE at the end of your source program This file causes your references to library symbols to be resolved so that your code can be assembled The second file is a binary file containing the code of the library routines You must present this to the assembler by giving its name in the LIBRARY option on the command line If you manage to leave out one of these two files or use a definition file that is not compatible with the binary file then undefined chaos will result You can build your own libraries ss follows a write the code b assemble it the output from the assembler is now the library binary file c build a definitions file from the symbol table listing resulting from the assembly for each symbol in the library which you wish to be able to access from programs write a line symbol EQU offset where offset is the value printed for
14. Manual 30 ROL lt length gt FOL lt length gt ROL W ROR lt length gt ROR lt length gt ROR W ROXL lt length gt ROXL lt length gt ROXL W ROXR lt length gt ROXR lt length gt FOXR W lt dreg gt lt dreg gt lt expr gt lt dreg gt lt ea gt lt dreg gt lt dreg gt ii lt expr gt lt dreg gt lt ea gt lt dreg gt lt dreg gt H lt expr gt lt dreg gt lt ea gt lt dreg gt lt dreg gt H lt expr gt lt dreg gt lt ea gt 68K ASM Assembler Bit Operations The length specification is optional on these instructions as the length must be long if the lt eas is a lt dregs and must be byte if the lt ea gt is anything else BCHG lt length gt lt dreg gt lt ea gt BCHG lt length gt lt expr gt lt ea gt BCLR lt length gt lt dreg gt lt ea gt BCLR lt length gt f lt expr gt lt ea gt BSET lt length gt lt dreg gt lt ea gt BSET lt length gt lt expr gt lt ea gt BTST lt length gt lt dreg gt lt ea gt BTST lt length gt lt expr gt lt ea gt Branch Instructions The branch instructions may optionally have an extent S or L coded as described at B 4 3 above B lt ee gt lt extent gt lt expr gt where lt ee gt cc CS EQ GE GT HI LE lt extent gt S L 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler B 5 8 B 5 9 B 5 10 B 5 1 The unconditional branch in
15. OST computer Systems Limited 68K ASM Assembler 68K ASM ASSEMBLER USER MANUAL Copyright 1984 GST Computer Systems Limited 68K ASM User Manual 1 8290 6 GST 68 1 03 GST Computer Systems Limited G K ASM Assembler CONTENTS INTRODUCTION Copyright Making a Backup Copy Notation Used in this Manual rero wmv HOW TO RUN THE ASSEMBLER Loading the Program Command Line Format Command Line Options D D wo Wher ASSEMBLER INPUTS AND OUTPUTS Control Inputs Source Inputs Library Input Screen Output Source Listing Symbol Table Listing Object Code Output RAG EWE CO w Co Co Co Co Ww Ww LISTING OUTPUTS Source Listing Symbol Table Listing FFE D H APPENDICES gt BIBLIOGRAPHY SOURCE LANGUAGE Lexical Analysis Source Language Line Format Expressions Addressing Modes Instructions Assembler Directives w w w w w w w AY Fw D H ERROR AND WARNING MESSAGES Error Messages Warning Messages Operating System Error Messages GAA O w DH 68K ASM User Manual 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler INTRODUCTION This manual tells you how to use 68K ASM which is the assembler for the 68K 0S operating system produced by GST Computers Syst ms Limited It tells you how to load and run the assembler what inputs the assembler takes and what outputs it produces how the assembler language instructions should be coded what assembler directives are avai
16. aracters long OE value stack underflow This is an internal assember error which should never occur OF invalid character Some characters such as have no meaning to the assembler They may only be used within strings The character is ignored 10 invalid shift operator The characters lt and gt are only legal as pairs in shift operators LES TU and Meg 11 no digits in number A number is expected eg after or but no digits are present 12 number overflow The fer is too large and will not fit in 32 bits 13 string terminator missing A string must be terminated by a quote character 14 relocatable value not allowed here Some addressing modes and directives require absolute values 15 multiply overflow in expression A multiply overflow error occurred while evaluating an expression 68K ASM User Manual ho 8290 6 GST 68 1 03 GS Computer Systems Limited 68K ASM Assembler 16 divide by O or divide underflow A divide error occurred during evaluation of an expression 18 ve value illegal Some directives eg DS can accept a zero or positive number but a negative value is illegal 19 value must be ve nonzero Some instructions or directives require a positive nonzero value eg the number of elements for DCB 1A value out of range This is a general purpose message for any value out of range in instructions or directives The actual value range depends on context
17. bol gt The symbol is one of an assembler directive a 68000 instruction 68K ASM User Manual 19 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler B 2 3 B 2 4 The Operand Field The syntax of the operand field depends on the operation lt white space gt terminates the operand The syntax of each format of the operand field is described below when the operation is defined The Comment Field When enough of the rest of the line has been processed to satisfy the operation for the majority of operations this is up to the first lt white space gt beyond the start of the operand field anything left on the line is deemed to be comment and ignored 68K ASM User Manual 20 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler B 3 Expressions Expressions are constructed from unary operators binary operators gt gt lt lt amp parentheses co operands lt symbol gt lt number gt lt string gt lt string gt s used in expressions must be four characters long or shorter The value of a lt string gt consists of the ASCII values of the characters right justified in the normal 32 bit value Thus for example the two expressions a 256 b and ab have the same value Note that the DC directive can use longer strings with different evaluation rules The character used as an expression operand has the same value as a lt label gt defined
18. by a lt file name gt then this is the name cf the lt listing gt output and the positional lt listing gt parameter if specified is not used the ERRORS option also sets the NOSYM option 68K ASM User Manual 5 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler LIST generate a full listing if the option is followed by a lt file name gt then this is the name of the lt listing gt output and the positional lt listing gt parameter if specified is ignored NOBIN do not generate any binary output BIN generate binary output if ihe option is followed by a lt file name gt then this is the name of the lt binary gt output file and the positional lt binary gt parameter if specified is ignored NOSYM do not generate a symbol table listing this is the default if ERRORS is specified SYM generate a symbol table listing this is the default if LIST is specified or if no listing options are specified if SYM and NOLIST are both specified then the SYM is ignored LIBRARY or LIB the LIBRARY option must be followed by a lt file name gt and specifies a file containing a precompiled library to be included in the assembly Where conflicting options are given the last one specified takes effect For example if LIST mydir fred list NOLIST ERRORS is specified then only an error listing is sent to MYDIR FRED LIST and if SYM ERRORS is specified then no symbol table output will be gene
19. defined register A register has been multiply defined in a multiregister sequence eg AO D1 D0 D3 has D1 multiply defined 43 decimal number goes negative A decimal number has a value between 80000000 and FFFFFFFF This is a perfectly valid number with which to do unsignec arithmetic but it is an overflow if the programmer was intending to use it for signed arithmetic As the assembler does not know what the programmer wants to do with the number it produces this warning hk nonzero SECTION not implemented Implementation restriction only one relocatable section is supported 45 value will be sign extended to 32 bits In MOVEQ the expression is between 80 and FF so it will be sign extended to a 32 bit negative value 46 nonstandard use of this instruction This warning is printed when an instruction is used in a nonstandard manner which may be a bug eg LINK with a positive displacement 47 branch could be short A forwards branch or a branch with an explicit L is within 128 bytes range and could be a short branch 48 END directive missing An END directive is expected at the end of the assembly but end of file was found instead 68K ASM User Manual 43 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler C 3 Operating System Errors When the assembler gets an error code from 68K OS it usually gives up completely first displaying a message relating to the error on the screen for
20. describes the system programmer s interface to 68K 0S and contains full details of how to write device drivers and other similar topics Available from GST Computer Systems Limited In addition the following is an excellent book which teaches assembler programming on the 68000 and also contains a complete deseription of the 68000 s instruction set It is suitable for the first time assembler programmer and is also very valuable to the experienced assembler programmer who has not used a 68000 before as it points out many of the common errors and pitfalls which usually cause trouble for the newcomer to the 68000 Programming the MC68000 by Tim King and Brian Knight Addison Wesley Available from GST Computer Systems Limited 91 High Street Longstanton Cambridge at 8 95 including postage and packing 68K ASM User Manual 16 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler B SOURCE LANGUAGE This appendix defines the source language accepted by the assembler It does not specify the details of the Motorola 68000 instruction set and a manual for the 68000 itself must be consulted for this information Lexical Analysis This section defines the way in which characters are combined to make tokens The notation used is described in section 1 above Generally a line of assembler source is civided into the traditional four fields of label operation operand an comment the fields being separated by spaces Thus space
21. elocatable the assembler will try to generate a PC relative address This will fail if the destination is too far away or if the effective address is required to be alterable in either case an error message will be produced and the programmer must find some other way of writing the program Forward references which are undefined at the time of meeting the symbol are assumed to be simple relocatable If the programmer wishes to reference an absolute address this can only be done by coding amp number or by coding a symbol which has previously been equated to a number For example MOVE B 80 SCREEN SCREEN EQU 18063 is not legal and will generate an error whereas JMP FRED FRED is legal and will generate a PC relative addressing mode An immediate operand lt expr gt where the lt expr gt is not absolute will probably generate wrong code as the assembler does not know where the code will be loaded and executed and is unable to add the necessary relocation base s Therefore the assembler will generate warning messages if a relocatable lt expr gt is used as an immediate operand Branch Instructions The branch instructions Bec BSR can use either an 8 bit PC relative displacement or a 16 bit displacement the assembler will correctly choose the most efficient option for a backwards reference but needs some help with forward references The default option is to generate a long 16 bit displacement These branch ins
22. git gt lt binary digit gt O 1 lt octal digit gt O 1 617 lt digit gt 0 1 819 lt hex digit gt lt digit gt al f Al F lt string gt lt stringchar gt lt stringchar gt where a lt stringchar gt is any ASCII character except a line feed a control character or a single quote in eddition a lt stringchar gt may be two adjacent single quotes which allows a single quote to be coded inside a string There are two types of lt symbol gt used by the assembler lt symbol gt s appearing in the operation field are operation type symbols and those appearing in the operand field are operand type symbols These two sets of lt symbol gt s are quite separate and there is no confusion except in the mind of the programmer between the same name used in both places Thus you can have user defined labels with the same names as instructions and directives if you really want to There are special forms of strings used by the INCLUDE and TITLE directives which allow the user to omit the enclosing quotes lt file name gt lt string gt lt non space character gt 1 i e a lt file name gt is either enclosed in quotes or is terminated by a space or end of line lt title string gt lt character gt i e a lt title string gt is terminated by end of line 68K ASM User Manual 18 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler B 2 Source Language Line Format B 2 2
23. gt lt expr gt lt string gt If a lt constant gt consists of a single string anc no other operators or operands then it is left justified in as many bytes words or long words depending on whether lt length gt is B W or L as necessary with the last word or long word padded with zero bytes as necessary Ir this case the lt string gt can be of any non zero length there is no restriction as there is with lt string gt s that form part of lt expr gt s 68K ASM User Manual 35 6290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler This leads to the rather strange feature that DC L at causes the character to be left justified whereas DC L a 0 is an lt expr gt and so causes the character to be right justified Note that other 68000 assemblers have even stranger features in this area In the case of DC W and DC L the current location counter is advanced to a word boundary if necessary and the the optional lt label gt is defined with this adjusted value Thus the code fragments FRED DC W TER and FRED DC W sis do not necessarily have the same effect as the second could result in FRED having an odd value depending on earlier use of DC B DS B or DCB B Expressions given as operands of DC directives must be absolute No more than six bytes of code generated by a DC are printed on the listing if all generated bytes are required then the constants must be coded on more separate D
24. his is en assembler internal error it should only happen if the source file has changec between pass 1 of the assembler and pass 2 05 missing operand The instruction requires two operands and only one has been coded 06 syntax error The line contains a syntax error which has left the assembler with very little idea of what was meant 07 syntax error in expression or operand The assembler is expecting an expression or other instruction operand but does not understand what it has found 08 multireg cannot mix Dreg amp Areg Data registers and address registers may not be combined in a range eg D3 A4 is illegal 09 multireg bad sequence The registers in a range must be in increasing order eg D5 D2 is illegal 8290 6 GST 68 1 03 Co O GST Computer Systems Limited 68K ASM Assembler OA unmatched open bracket There ere too many open brackets in the expression unmatched open brackets are closed at the end of the expression OB unmatched close bracket There are too many close brackets in the expression unmatched close brackets are ignored OC expression too complicated An expression is limited to five levels of nested brackets Certain combinations of operators car cause this error with fewer brackets eg when low priority operators are followed by high priority operators OD expression string too long When a string is used as a term in en expression it may be up to four ch
25. ill default to 66 To obtain essentially unpaginated output the user may set PAGELEN to a very large number in which case only one title will be printed at the beginning of the listing and form feeds will be included at the start and end of the listing and between the source and symbol table listings only The format of each printed page is lt heading gt lt blank gt lt title gt lt blank gt lt blank gt lt listing gt lt form feed gt where lt blank gt is a blank line i e a line feed character lt heading gt is a line containing the name and version of the assembler the name of the source file being assembled the page number and the time and date lt title gt is the lt title string gt given on the relevant TITLE directive if no relevant TITLE directive has been coded then this line is lt blank gt lt listing gt consists of PAGELEN 14 lines of listing of whatever format is appropriate source listing or symbol table listing lt form feed gt is the ASCII form feed character and appears immediately after the line feed which terminates the last line if any of lt listing gt 68K ASM User Manual 12 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler Ad Source Listing Note that if the ERRORS option has been requested then not all source lines are listed only lines containing errors are listed together with the error messages Each line of listed source code has the foll
26. l gt is assigned the value of the adjusted location counter The first lt expr gt must be amp bsolute and contain no forward references and is the number of storage units bytes words or longs to be initialised and the second lt expr gt is the value to be stored in each of these storage units The second lt expr gt should be absolute PAGE Start New Listing Page The directive PAGE causes the next line of the listing to appear at the top of the next page The PAGE directive itself is not listed 68K ASM User Manual 37 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler B 6 11 B 6 12 B 6 13 B 6 14 B 6 15 PAGEWID Define Width of Page The directive PAGEWID lt expr gt defines the width of the printed output to be lt expr gt characters The lt expr gt must be absolute and contain no forward references and must be between 72 and 132 inclusive If no PAGEWID directive is present the default is 132 characters PAGELEN Define Length of Page The directive PAGELEN lt expr gt defines the length of each listing page to be lt expr gt lines The lt expr gt must be absolute and must contain no forward references The value given is the physical length of the paper rather fewer lines of assembler source are actually listed on each page LIST Switch Listing On The directive LIST restarts listing that was suppressed by a previous NOLIST directive The LIST directive itself is
27. lable what they do anc how to code them It does not include a detailed description of the instruction set of the Motorola MC68000 processor family for which you will need additional documentation tell you how to talk to 68K OS for which you will have to consult the 68K OS Programmer s Manual teach programming in general teach assembler programming or 68000 programming in particular Appendix contains a list of some other publications which you may find helpful Copyright This manual and the 68K ASM assembler software are Copyright 1984 GST Computer Systems Limited and may not be copied by any means whatsoever without prior written permission from GST Computer Systems Limited Permission is hereby granted to make copies of the software for security or backup purposes only Making a Backup Copy It is strongly recommended that you make a backup copy of the supplied tape before using the assembler The procedures for doing this are fully described in the 68K 0S User Manual First you take a blank tape and format it using the 68K 0S FORMAT program Then COPY every file on the supplied assembler tape to the newly formatted blank tape We suggest that you use the new tape for running the assembler and keep the supplied tape as the backup copy 68K ASM User Manual 3 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler 1 3 Notation Used in this Manual This section describes the notation used
28. mbler EOR lt length gt lt dreg gt lt ea gt EOR lt length gt f lt expr gt lt ea gt EORI lt length gt f lt expr gt lt ea gt NOT lt length gt lt ea gt OR lt length gt lt ea gt lt dreg gt OR lt length gt lt dreg gt lt ea gt OR lt length gt f lt expr gt lt ea gt ORI lt length gt f lt expr gt lt ea gt There are special forms of the ANDI EORI and ORI instructions which operate on the status register AND B H lt expr gt SR AND W H lt expr gt SR AND B lt expr gt CCR ANDI B i lt expr gt SR ANDI W H lt expr gt SR ANDI B H lt expr gt CCR EOR B lt expr gt SR EOR W lt expr gt SR EOR B lt expr gt CCR EORI B lt expr gt SR EORI W lt expr gt SR EORI B lt expr gt CCR CR B lt expr gt SR OR W lt expr gt SR OR B lt expr gt CCR ORI E lt expr gt SR ORI W i i lt expr gt SR ORI B lt expr gt CCR Bi eh Shift Operations ASL lt length gt lt dreg gt lt dreg gt ASL lt length gt H lt expr gt lt dreg gt ASL W lt ea gt ASR lt length gt lt dreg gt lt dreg gt ASR lt length gt lt expr gt lt dreg gt ASR W lt ea gt LSL lt length gt lt dreg gt lt dreg gt LSL lt length gt H lt expr gt lt dreg gt LSL W lt ea gt LSR lt length gt lt dreg gt lt dreg gt LSR lt length gt H lt expr gt lt dreg gt LSR W lt ea gt 68K ASM User Manual 29 6290 6 GST 68 1 03 GST Computer Systems Limited B 5 7 68K ASM User
29. n the file or subsequent lines then this will be ignored by the assembler The syntax of the end statement is END 68K ASM User Manual 34 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler B 6 5 B 6 6 EQU Assign Value to Symbol Syntax lt label gt EQU lt expr gt The lt expr gt is evaluated and the value is assigned to the lt symbol gt given in the lt label gt The lt expr gt may not include references to any symbol which has not yet been defined The value of the defined symbol is absolute simple relocatable or complex relocatable depending on the type of the lt expr gt REG Define Register List Syntax lt label gt REG lt multireg gt The lt symbol gt given in the lt label gt is defined to refer to the register list given in lt multireg gt and may be used in MOVEM instructions only The purpose of this directive is to allow a symbol to be defined which represents a register list pushed at the start of a subroutine so that the same list of registers can be popped at the end of the subroutine without the risks involved in writing the list out twice DC Define Constants This cirective defines constants in memory Memory is reserved and the values of the constants given are stored in this memory This facility is intended to allow constants and tables to be created Syntax lt label gt DC lt length gt lt constant gt lt constant gt where lt constant
30. of a path name for 68K 0S 68K ASM User Manual 33 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler B 6 2 B 6 3 B 6 4 SECTION Start Relocatable Section This directive defines the relocation base to be used for subsequent code generation The only section implemented is section 0 No SECTION directive need be coded unless OFFSET is used in which case a SECTION directive must separate sequences of OFFSET definitions from following code Any number of SECTION directives may be present The syntax of the SECTION directive is SECTION lt expr gt where the expression must be absolute contain no forward references and have the value zero OFFSET Define Offset Symbols The OFFSET directive provides a means for symbols to be defined as offsets from a given point this is particularly useful for defining field names for data structures The lt expr gt given in an OFFSET directive must be absolute and must not contain forward references or external references The value of the lt expr gt is the initial value of a dummy location counter which can then be used to cefine labels on following DS directives The syntax of the OFFSET directive is OFFSET lt expr gt Between an OFFSET directive and a following OFFSET or SECTION or END directive the following are not allowed DC DCB instructions END End of Program The END directive defines the end of the source input if there is anything else i
31. of the source listing starting on a new page Object Code Output The assembler produces a binary file which can be loaded and run directly as a 68K 0S program provided that you have coded the required control information the Program Header Block at the start of the program For details consult the 68K 0S Programmer s Reference Manual Alternatively the output binary file from the assembler can be amp library file which is not directly executable but can be included in future assemblies There is no difference between the format of a library file and the format of an executable program file the differences are contained entirely in the code you write 68K ASM User Manual 11 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler L Listing Outputs There are two listings produced by the assembler the source listing and the symbol table listing Each line of listing output produced can be up to 132 characters long excluding the terminating newline in particular each title line is 132 characters long Some printers cannot be made to print 132 characters to a line sc the PAGEWID directive is provided to specify the actual width of the printer Any line longer than FAGEWID characters will be overflowed onto the following line and these overflows will be taken account of when determining whether a page is full The listing output is paginated with the total page length defined by the user in a PAGELEN directive or w
32. on the line in which the is used would have The syntax of an expression is then lt expr gt lt symbol gt lt number gt lt string gt lt expr gt lt expr gt lt expr gt lt expr gt lt binaryop gt lt expr gt lt binaryop gt lt lt gt gt amp The operators have the following meanings unary the value of the operand is unchanged unary the value of the operand is negated Note that all operands are regarded as 32 bit values these values are obtained by extending the original operand on the left with zeroes all operands are originally positive except that symbols can be defined to have negative values in which case they will already be 32 bit negative numbers Likewise all intermediate and final results from expressions are calculated as 32 bit values and are truncated as necessary according to context just before being used binary addition binary subtraction multiplication 68K ASM User Manual 21 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler division the result is truncated towards zerc lt lt shift left the left operand is shifted to the left by the number of bits specified by the right operand which should be an absolute value between O and 32 inclusive otherwise the result is undefined vacated bits at the right hand end are filled with zeroes gt gt shift right as for shift left but the operand is shifted right
33. ormation for the assembler is supplied by the user typing a command line on the keyboard The command line is described in section 2 above and specifies where all the other input and output files and devices are Source Inputs The assembler assembles one main source file This may direct the assembler using INCLUDE directives to read other source files When assembling large and complicated programs it is normal to put no real code at all in the main source file which will just contain INCLUDE directives naming the other source files For example TITLE A large complicated assembly Start with the 68K 0S parameter file then the parameter file for my program INCLUDE system 68kos in INCLUDE myparms in Now the main code to be assembled this is rather large so it is split into two separate files INCLUDE progl in INCLUDE proge2 in Finally the LIBRARY facility is being used to include a library of useful subroutines the declaration file for the library must be INCLUDEA last INCLUDE library in END It is recommended that filenames of main source files end in ASM but this is not a requirement and you can call them anything you like It is recommended that filenames of INCLUDEd files end in IN but this is not a requirement and you can call them anything you like Note that 68K ASM will search for any INCLUDEd files on the default data directory unless a directory is specified within the INCLU
34. owing format Columns Field contents Format 1 4 line number k digit decimal 5 blank 6 section number l digit hex 8 15 location counter 8 digit hex 16 blank 17 28 generated code up to 12 digits hex 29 blank 30 132 source line as coded truncated to fit Source line numbers start at 1 for the first line in the main source field and are incremented by 1 for each source line processed regardless of the file from which it came and regardless of whether the line is listed or not The section number is zero for instructions and data assembled into section zero It is left blank when absolute addresses such as those generated under the influence of an OFFSET directive are being displayed For instructions and data definition directives the location counter field contains the address which woulc be assigned to a label defined cn that source line note that this is not necessarily the same as the value of the location counter after the previous line has been processed For other directives containing expressions whose value is likely to be of interest to the user e g OFFSET EQU the value of the expression is printed in the location counter field or the code field as appropriate If there is nothing useful that can be printed in this field then it is left blank The generated code field contains up to 6 bytes of code generated by an instruction or a data definition directive DC or DCB If an instruction generates more than 6
35. r constructs the lt binary gt lt file name gt by taking the lt source gt lt file name gt end replacing the file extension with BIN Examples FRED assemble FRED ASM put a full listing with symbol table listing in FRED LIST and put the binary in FRED BIN FRED TXI nobin assemble FRED ASM print the listing as it is produced and don t generate any binary FRED errors BIN other fred bin assemble FRED ASM send an error listing only with ro symbol table to FRED LIST and put the binary in OTHER FRED BIN note that coding OTHER FRED would not have achieved this FRED txl other fred bin errors sym LIBRARY system 68kos lib assemble FRED ASM print an error listing plus symbol table directly put the binary in OTHER FRED BIN and include the precompiled file SYSTEM 68KOS LIB in the output binary When the assembly has finished and if there have been no operating system errors the assembler will not terminate but will repeat the prompt asking for a command line You can now do another assembly without having to reload the assembler When you have done all the assemblies that you want you may reply to this prompt with ENTER and the assembler will terminate 68K ASM User Manual 7 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler Ww QW j ASSEMBLER INPUTS AND OUTPUTS This chapter describes all the input and output files end devices that the assembler can use Control Inputs Control inf
36. r field contains blank symbol is absolute 0 symbol is simple relocatable and lives in section O X symbol is complex relocatable R symbol is a register list defined by a REG directive If the symbol is undefined then the section number and value fields will contain the word undefined The line number field contains the line number of the first line in which the symbol was defined for an undefined symbol it is left blank 68K ASM User Manual 15 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler A BIBLIOGRAPHY In order to write 68000 assembler programs that run under the 68K 0S operating system you will need the following two publications or equivalents MC68000UM AD3 16 Bit Microprocessor User s Manual This Motorola publication describes the architecture and instruction set of the MC68000 family of processors It is available from GST Computer Systems Limited 91 High Street Longstanton Cambridge at 8 95 including postage and packing 9992 1 GST 13 68K OS Programmer s Reference Manual This manual describes the features of the 68K 0S operating system and defines the system calls useful to the ordinary applications programmer and other interactions between the operating system and user s programs It is supplied with the O8K 0S operating system In order to make more advanced use of 68K 0S the following additional manual is required 9992 1 GST 54 68K OS System Programmer s Manual This manual
37. rated The minimum command line just consists of the name of the input source file In this case a full listing with symbol table is generated i e the default is LIST SYM to the file whose name is constructed from the lt source gt lt file name gt as described below Also by default a binary output file is generated i e the default is BIN to the file whose name is constructed from the lt source gt lt file name gt as Gescribed below The lt source gt file name is examined if it does not contain a file extension component then ASM is appended to the given name to make the name of the actual source file used The name of the lt listing gt file may be given positionally as the second parameter or may be specified explicitly after a ERRORS or LIST option or may be allowed to default If no lt listing gt lt file name gt is given in a ERRORS or LIST option and no NOLIST option has been specified then the assembler constructs the lt listing gt lt file name gt by taking the lt source gt lt file name gt and replacing the file type with LISI 68K ASM User Manual 6 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler The name of the lt binary gt file may be giver positionally as the third parameter or may be specified explicitly after a BIN option or nay be allowed to default If no lt binary gt lt file name gt is given in a BIN option end no NOBIN option has been coded then the assemble
38. s Thus the listing generated by ERRORS is more or less the same as the listing generated by LIST if NOLIST directives are in force throughout If there is no END directive a special warning message is printed relating to this at the end of the assembly the line number in this warning message is one greater than the number of the last line in the input file At the end of the assembly a summary of the number cf errors and warnings generated is output both to the listing if there is one and to the screen 68K ASM User Manual 1h 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler 4 2 Symbol Table Listing The symbol table listing is a sorted list cf each user defined symbol with its type value and line number of the line on which it was first defined The listing is sorted alphabetically on symbol name with ASCII collating sequence for non alphabetic characters It is printed in a single column The symbol table listing for each symbol contains the following fields Columns Field contents Format 3 8 symbol up to 8 characters 9 blank 10 13 symbol type see below 14 blank 15 section number G or Z or R see below 16 blank 17 24 value 8 digit hex 25 blank 26 29 line number L digit decimal The type field contains MULT if the symbol is multiply defined the assembler will use the first definition and print error messages for subsequent ones blank ordinary labels The section numbe
39. s are significant in this language apart from just terminating symbols As a special case a line containing an esterisk or semicolon in column one consists entirely of comment and is treated as a blank line Any syntactic token is terminated either by the first character which cannot form part of that token or by end of line lt syntactic token gt lt white space gt lt symbol gt lt number gt lt string gt lt newline gt Seri ss wag sel CLD Lee e where lt newline gt is a line feed character lt white space gt lt space gt lt space gt where lt space gt is the ASCII space character lt symbol gt lt start symbol gt lt rest symbol gt lt start symbol gt lt letter gt lt rest symbol gt lt letter gt lt digit gt _ lt letter gt alb ly zlA Bl ly z s note that outside strings whether a letter is upper or lower case is not significant note that a symbol can be any length but only the first eight characters are significant 68K ASM User Manual 17 8290 6 GST 68 1 03 GS Computer Systems Limited 68K ASM Assembler lt number gt lt binary number gt lt octal number gt lt decimal number gt lt hex number gt lt binary number gt lt binary digit gt lt binary digit gt lt octal number gt octal digit gt lt octal digit gt 1 lt decimal number gt lt digit gt lt digit gt lt hex number gt lt hex digit gt lt hex di
40. struction is BRA lt extent gt lt expr gt and is in fact a version of the conditional branch instruction that means branch regardless of the condition codes The branch to subroutine instruction is BSR lt extent gt lt expr gt Trap Instructions Grouped here are those instructions whose main purpose is to generate traps either conditionally or unconditionally CHK W lt ea gt lt dreg gt TRAP lt expr gt TRAPV The DBcc Instruction This instruction is a looping primitive it tests the condition codes as does the Bee instruction but also allows the conditions always true and always false to be tested DB lt dbee gt W lt dreg gt lt expr gt where lt dbee gt lt cc gt T F RA RA is a synonym for F meaning branch regardless of the condition codes thus the instruction DBRA loops without testing conditions other than the value of the loop counter Jump Instructions The jump instructions are an unconditional jump and a subroutine call JMP lt ea gt JSR lt ea gt See section B 4 2 for a definition of how the assembler interprets lt expr gt as an lt ea gt as that paragraph is particularly relevant to these two instructions Stack Frame Management LINK lt areg gt H lt expr gt UNLK lt areg gt 68K ASM User Manual 3L 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler B 5 12 Odds and Ends NOP RESET RTE RTR RTS TAS B lt ea gt STOP H lt e
41. the symbol on the listing You can extend libraries in the obvious way as the assembly in step b above can itself use a library 68K ASM User Manual io 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler 3 4 Screen Output 3 5 In addition to the identification message and command line prompt when the assembler starts the following are output to the screen The assembler makes two passes of the source input files and will tell you when it starts each pass The second pass can be expected to take a lot longer than the first pass if listings and or binary output are wanted The symbol table listing is produced after the summary messages are displayed so if you are assembling a large program it will be an appreciable time after the summary messages are displayed before the assembler finishes completely A summary of the number of errors and warnings generated is written to the screen together with a summary of the amount of memory used This memory size excludes the memory occupied by the code of the assembler itself about 17k and the assembler s initial data space about 6k You can get a good idea of how complex your assemblies are and whether you are likely to run out of memory by watching the memory use figure If you do several assemblies in one go without reloading the assembler then the assembler will re use any memory it has obtained from the operating system but will not release any memory until it
42. they all operate on a single length of operand and the operand length is optional These are MOVE W lt ea gt CCR MOVE W lt ea gt SR MOVE W SR lt ea gt MOVE L lt areg gt USP MOVE L USP lt areg gt The MOVEM and MOVEP instructions are also involved with data movement but are not generated automatically by the assembler from the MOVE mnemonic Their syntax is MOVEM lt length gt lt multireg gt lt ea gt MOVEM lt length gt lt ea gt lt multireg gt MOVEP lt length gt lt dregs lt expr gt lt areg gt MOVEP lt length gt lt expr lt areg gt lt dreg gt The other data movement instructions are EXG L lt reg gt lt reg gt where lt reg gt lt areg gt lt dreg gt LEA L lt ea gt lt areg gt PEA L lt ea gt SWAP W lt dreg gt B 5 3 Arithmetic Instructions In a simlar way to the MOVE instruction mnemonics are generic and will generate ADDA SUBA CMPI CMPM CMP and SUB ADDQ CMPA the explicit the ADD ADDI again SUBI SUBQ if necessary forms can be coded if desired ADD lt length gt CMP lt length gt SUB lt length gt 68K ASM User Manual lt ea gt lt ea gt lt ea gt lt ea gt lt ea gt lt ea gt 27 8290 6 GST 68 1 03 GST Computer Systems Limited ADDA lt length gt ADDI lt length gt ADDQ lt length gt CMPA lt length gt CMPI lt length gt CMPM lt length gt SUBA lt length gt SUBI lt length gt SUBQ lt length gt Addi
43. throughout the manual to describe syntax of assembler source as well as other items means that the expression on the right defines the meaning of the item on the left and can be read as is ee angle brackets containing a lower case name represent a named item which is itself made up from simpler items such as lt decimal number gt a vertical bar indicates a choice and can be read as or is square brackets indicate an optional piece of syntax that may appear O or 1 times curly brackets indicate a repeated piece of syntax that may appear O or more times se is used informally to denote an cbvious range of choices as in lt digit gt O0 1 8 19 Other symbols stand for themselves Example lt binary number gt lt binary digit gt lt binary digit gt lt binary digit gt oll ll means that a binary number is a sign followed by a binary digit followed by any number of further binary digits where a binary digit is the character O or the character l Some examples of binary numbers are 0 1010101100 0000000000000 Some of the special symbols used in the syntax notation also occur in the assembler source input and the common sense of the reader is reliec on to distinguish these as in for example lt operator gt lt lt 68K ASM User Manual 4 8290 6 GST 68 1 03 a Gorapuiter E E 68K ASM Assembler 2 1 2 2 2 3 HOW TO RUN THE ASSEMBLER Loading the Program
44. tional binary ADDX lt Length gt ADDX lt length gt CLR lt length gt DIVS W DIVU W EXT lt length gt MULS W MULU W NEG lt length gt NEGX lt length gt SUBX lt length gt SUBX lt length gt TST lt length gt 68K ASM Assembler lt ea gt lt areg gt f lt expr gt lt ea gt H lt expr gt lt ea gt lt ea gt lt areg gt H lt expr gt lt ea gt lt areg gt lt areg gt lt ea gt lt areg gt H lt expr gt lt ea gt H lt expr gt lt ea gt arithmetic instructions are lt dreg gt lt dreg gt lt areg gt lt areg gt lt ea gt lt ea gt lt dreg gt lt ea gt lt dreg gt lt dreg gt lt ea gt lt dreg gt lt ea gt lt dreg gt lt ea gt lt ea gt lt dreg gt lt dreg gt lt areg gt lt areg gt lt ea gt The binary coded decimal instructions are written as follows ABCD B ABCD B NBCD B SBCD B SBCD B B 5 4 Logical Operations AND EOR OR are generic mnemonics that will generate ANDI ORI as necessary AND lt length gt AND lt length gt AND lt length gt ANDI lt length gt 68K ASM User Manual lt dreg gt lt dreg gt lt areg gt lt areg gt lt ea gt lt dreg gt lt dreg gt lt areg gt lt areg gt EORI lt ea gt lt dreg gt lt dreg gt lt ea gt f lt expr gt lt ea gt fH lt expr gt lt ea gt 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Asse
45. tructions can have an explicit extent coded of S short meaning that an 8 bit displacement is to be used or L long meaning that a 16 bit displacement is to be used for example BNE S FRED FRED is not very far away 68K ASM User Manual 25 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler B 5 Instructions This section lists all the 68000 instruction mnemonics describes how the various modifiers are coded and defines the operand syntax of each instruction Note however that for precise details of the actual addressing modes etc legal for each instruction a manual for the Motorola 68000 should be consulted An instruction may optionally have a lt label gt Before any code for an instruction is generated the current location counter is advanced to an even address if not already even and it is this adjusted address that is assigned to the lt symbol gt in the lt label gt Beil Instruction Mnemonic Format The operation field of a source line containing a machine instruction is simply a lt symbol gt However there is some flexibility allowed in the coding of mnemonics as there are some generic mnemonics that relate to a group of instructions the actual instruction wanted being chosen by the assembler depending on the operands coded Instructions which may operate on operands of different lengths must have the length of the operand coded as part of the lt symbol gt this takes the form of B W or L as
46. ut of range BRA S or some other Branch S has been coded but the destination is more than 128 bytes away 26 long branch out of range The destination of a long branch must be within 32k 27 value must be simple relocatable The expression should be simple relocatable absolute or complex values are illegal e g in the destination of a branch instruction 28 value must not be complex Absolute and simple relocatable expressions cen generally be used as addresses but a complex relocatable value is illegal 29 this directive must have a label EQU and REG require a label 2A unable to generate position independent code here Normally if a label or expression is used to specify an address in an instruction a PC relative addressing mode is generated to produce position independent code This is not an alterable addressing mode so this error message is generated when an alterable addressing mode is required 2B short branch to next instruction NOP generated A short branch to the next instruction is not a legal 68000 opcode The assembler generates a NOP instruction in this case 68K ASM User Manual ho 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler es A Warning Messages hO size missing W assumed No size was specified on an index register 4 size missing W assumed The instruction or directive can have more than one size but no size was specified 42 multiply
47. xpr gt The Sce instruction has the same set of conditions as DBcc but not the RA synomym S lt see gt B lt ea gt where lt sce gt lt ce gt T F 68K ASM User Manual 32 8290 6 GST 68 1 03 GST Computer Systems Limited 68K ASM Assembler B 6 Assembler Directives Assembler directives are instructions to the assembler and with the exception of DC and DCB do not directly generate any code The directives provided are summarised below The The The The B 6 1 following directives must not have labels INCLUDE read another source file SECTION relocatable program section OFFSET define offset symbols END end of program following directives require labels EQU assign value to symbol REG define register list following directives may optionally have labels DC define constants DS reserve storage DCB define constant block following are listing control directives and must not have labels PAGE start new listing page PAGELEN define length of page LIST switch listing on NOLIST switch listing off TITLE define title for listing INCLUDE Read Another Source File This directive causes the named file to be read as if it were present in the original source file in place of the INCLUDE directive INCLUDE directives may be nested to at least three levels The syntax of an INCLUDE directive is INCLUDE lt file name gt where lt file name gt with optional surrounding quotes is the normal syntax
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