Rasm51E Cross Assembler for the 8051 Microcontroller User`s
Contents
1. nested The number of such nestings is limited only be the amount of dynamic memory available FUNCTIONS There are two built in functions highQ and low They return the high byte and the low byte of a word two byte expression respectively CONSTANTS Constants may be decimal binary octal hexadecimal or ASCII Hexadecimal constants must start with a numerical digit between 0 and 9 The suffixes b o d and h are used to denote binary octal decimal and hexadecimal constants respectively If no suffix is present the constant is assumed to be decimal ASCII constants are placed within single quotation marks See the following examples 10 10d 10D Oah OaH OAh OAH 120 120 1010b 1010B all have the value 10 A has the value 65 or 41h EXAMPLE Run Rasm51E with the example code DEMO ASM given below Try the l and Ix options and observe the LST files generated in each case Also try the d and dx options DEMO ASM will not assemble with the c option since some symbols are written without regard to cases e g One and one value equ 6 2 3 2 3 mov a value mov a high value 100h mov b low value 100h mov a high value 100h mov b low value 100h l1 mov a five two one two three four five five five five five anl a One 12 orl a oNe 13 org 8000h 14 orl b ONE org 0a00h include demo1 inc end of file first level include file one equ 1 two equ o2. Rasm51E Cross Assembler for the 8051 Microcontroller User s Manual 6 115 Microcomputer Laboratory Massachusetts Institute of Technology Department of Electrical Engineering and Computer Science The RASMS1E software is provided courtesy of Rigel Corporation Software and some parts of this manual copyright 1991 1994 Rigel Corporation Introduction Rasm51E is a cross assembler for the Intel MCS 51 assembly language used by the 8031 8051 family of microcontrollers A cross assembler is a piece of software that runs on one computer and produces code for another In 6 115 we will use IBM PC style computers running Windows to run Rasm51E We use an editor notepad emacs etc on the PC to write code in assembly language for the 8051 microcontroller Rasm51E produces a lower level Intel hex file We use Hyperterminal to download this hex file to the R31JP microcontroller development board that we will use in 6 115 Rasm51E is a two pass assembler Forward references are resolved during the second pass Using Rasm51e on the PC In 6 115 we will be programming our R31JP microcontroller board in assembly language You can write your program in any text editor Emacs vi edit Notepad etc but be sure to save it as a asm file On the 6 115 laboratory computers you will run Rasm51E in a DOS window We have written a batch file for you that calls Rasm51E with a few useful command line parameters You will see this batch file demonstr
3. ated during your laboratory familiarization The batch file is called RASM and includes a flag to generate a list Ist file The list file can be useful to you when debugging a program please take the time to look at this file for a code example and also look at the other files Rasm51E can produce to help you The description below explains the command line options that you can use with Rasm51E if you want different behavior or information from that provided by our RASM batch file Rasm51E has a few options activated by the command line parameters Invoke Rasm51E from DOS by typing Rasm51E filename asm c dl dx hl h1l h2 ll lx o s Note that the command line parameters as well as the asm extension are optional The command line parameters are described below COMMAND LINE OPTIONS c case sensitive labels The c option causes the assembler to save the labels and symbols in a case sensitive fashion Thus Labell and labell for example are interpreted as two different labels d display assembly progress The d option displays the progress of the assembler on the standard output device which by default is the screen The output may be redirected to another device or file For example Rasm51E myprog asm d gt myprog out redirects the progress report to the file myprog out Similarly the output may be redirected to a port Rasm51E myprog asm d gt prn redirects the progress report to the standard print device conne
4. cific op code The flag acc is shorthand recognized by the assembler which causes the assembler to substitute the actual hex numbered address for the accumulator OEOh into the code during assembly Using acc results in the use of a different mov op code than does the use of A The use of A in this case will result in smaller code explain why Some commands that we might like to use do not have an A version For example it is not possible to use the command push A to push the value of the accumulator on the stack This op code does not exist and the line of code will assemble with an error It is perfectly fine to use this line of code however push acc Using mov Make sure that when you write your programs you use movx or move when appropriate Consult your 8051 manual if you are in doubt as to which one you should use This can make errors in your program that prevent it from working properly but rasm will not always catch it It is always good to check that no errors occurred during assembly Sometimes an error message will appear but at the end rasm will still say no errors found This can cause you to not notice errors and make other changes that do not fix the problem Always check the lines above the no errors found line Labels and Reserved Words When using a jump or a call it is important that you do not use certain reserved words as the name of the subroutine you ar
5. cted to LPT1 parallel port 1 and Rasm51E myprog asm d gt Ipt2 redirects the progress report to the second parallel port LPT2 See your DOS manual for further information on output redirection dx extended display assembly progress This option is similar to the d option It gives further information about the assembly process For example it notifies if a label was resolved during the first pass or during the second pass See option d to redirect the output h1 hold terminate on pass 1 errors When used the h1 option prevent the assembler from proceeding with the second pass Note that Pass 1 errors does not include forward references not resolved during the first pass Unrecognized operations operands or pseudo operations illegal labels and fatal errors such as memory allocation or file creation errors are reported during the first pass This is a useful option to check a long source code for possible errors before generating a list file hor h2 hold terminate on after pass 2 errors When used the h or h2 option prevent the assembler from creating a LST or OBJ file 1 write regular lst file This option causes the creation of a LST file The LST file will have the same name as the source assembly file and the extension lst If the file already exists it will be overwritten Any include files specified in the source code will not be listed in the LST file Ix write extended Ist file descends into include fil
6. e referencing Jumps and calls can take constant values so if you make a forward reference to a label with the same name as a predefined constant value then the constant value will be substituted in assembler pass 1 rather than the usual substitution in pass 2 Therefore in addition to any constants you ve defined for yourself there are a number of label names that you should avoid These reserved words are listed below One easy way to do this would be to prefix all of your labels with a letter like L acc acc 0 acc 1 acc 2 acc 3 acc 4 acc 5 acc 6 acc 7 b b 0 b 1 b 2 b 3 b 4 b 5 b 6 b 7 cprl2 ct2 cy dph dpl ea es et0 etl ex0 exl exen2 exf2 exti0 extil fO ie ie 0 ie l ie 2 ie 3 ie 4 ie 5 ie 6 ie 7 ie0 iel int0 intl ip ip 0 ip 1 ip 2 ip 3 ip 4 ip 5 ip 6 ip 7 itO itl ov p pO p0 0 p0 1 p0 2 p0 3 p0 4 p0 5 p0 6 p0 7 pl p1 0 p1 1 pl 2 p1 3 p1 4 p1 5 p1 6 p1 7 p2 p2 0 p2 1 p2 2 p2 3 p2 4 p2 5 p2 6 p2 7 p3 p3 0 p3 1 p3 2 p3 3 p3 4 p3 5 p3 6 p3 7 pcon ps psw psw 0 psw 1 psw 2 psw 3 psw 4 psw 5 psw 6 psw 7 pt0 ptl px0 pxl rb8 rcap2h rcap2l rclk rd ren reset ri sbuf scon scon 0 scon 1 scon 2 scon 3 scon 4 scon 5 scon 6 scon 7 sint sm0 sml sm2 sp t0 tl t2con t2con 0 t2con 1 t2con 2 t2con 3 t2con 4 t2con 5 t2con 6 t2con 7 tb8 telk tcon tcon 0 tcon 1 tcon 2 tcon 3 tcon 4 tcon 5 tco
7. es This option is similar to the l option Any include files specified in the source code will be listed in the LST file that is the LST file will descend into the include files O write obj file in Intel Hex format This option causes the creation of a OBJ file in the Intel hex format The OBJ file will have the same name as the source assembly file and the extension obj If the file already exists it will be overwritten S generate symbol list appended to Ist file When invoked this option will generate a list of labels and symbols specified in the source assembly file The label and symbol lists will be appended to the LST file PSEUDO OPERATIONS There are three pseudo operations recognized by Rasm51E These are db define byte dw define word and org origin pseudo operations COMPILER DIRECTIVES The only compiler directive is the include directive used as include filename ext where filename ext must be found in the current directory or path The file filename ext will be opened and merged with the source assembly code The number of include files is limited by the DOS parameters BUFFERS and FILES See your DOS manual for further details Up to 8 include file may be nested That is include files may be specified inside include files stacked up to 8 levels EXPRESSIONS The four basic arithmetic operations are supported Parentheses may be used to group terms of an expression The Parentheses may be
8. mbler must begin with a number not a letter If the assembler finds something that you think is a number but that in fact begins with a letter it will interpret the number as a text word and become confused Make it clear to the assembler that you mean a number by beginning the number with a digit even for hex numbers For example 0AOh where the h specifies hex will be fine Here s another example an attempt to put a number directly into the accumulator If you wanted the actual number FF to be in the accumulator you would use the following command mov a 0FFh Remember that when you want to use a number always put a digit at the beginning of it For example if you tried to perform the previous operation by writing mov a FFh you would receive an error message from the assembler A versus ACC The accumulator is a commonly used register in assembly language programs Sometimes we refer to the accumulator with A for example mov A P2 On the other hand we can also refer to the accumulator with ACC For example the same result can be achieved with the line of code mov acc P2 Even though these two lines are legitimate and will assemble and will achieve the same result they are not the same assembly language instruction The command mov A is an actual single op code in the 8051 assembly language We can use the shorthand A to refer to the accumulator in this case because it is part of a spe
9. n 6 tcon 7 tfO tf1 tf2 thO thl th2 ti timerO timer1 tlO tll tl2 tmod trO trl tr2 txd wr The EQU Directive All EQU definitions must occur near the top of the assembly file before you use the definition Constants defined with equ should not start with R or r When such constants are used by inc or dec instructions for example RASM incorrectly reserves three bytes for the instruction even though it only takes two The third byte does not get filled and will contain unknown data when you download it BAD assembles to 15 55 00 ref equ 55h dec ref nop OK assembles to 15 55 00 xref equ 55h dec xref nop
10. ne one three equ one two include demo2 inc second level include file four equ two two five equ two three RASM Batchfile To assemble a program on the 6 115 lab computers with the RASM batch file open a command prompt change into the directory containing your asm file and type rasm filename asm RASM will create the Intel HEX format object file filename obj in the current directory This is the file that you will download to your R31JP with Hyperterminal TIPS There are several things that you should keep in mind when writing your programs If you re having trouble assembling your code i e if RASM is reporting errors or not completing assembly then you should double check your code Some problems to look for include File names Filenames should be limited to no more than 8 characters Numbers Make sure that you understand what you are trying to do when working with numbers in assembly language When you use a number such as the hexadecimal number AO letter A followed by a zero RASM Rasm51E will interpret the number based on the context of the instruction you are using Consider for example the following six lines of code all of which are an attempt to move the contents of Port 2 into the accumulator mov A OxO0AOh mov A 0AOh mov A P2 mov acc OAOh mov acc P2 mov A A0h The sixth line in bold mov A AOh will generate an error when assembled by RasmSle Numbers for the asse
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