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Pick-Poke-It2004-07

1. WHAT IF YOU CAN T LOAD PICK POKE IT A few PLUS D users are still using Version 1 of the ROM which was used in PLUS D s sold in December 1987 January 1988 Pick POKE It won t work with the version 1 ROM If you find that Pick POKE It doesn t work check the serial number on the bottom of your PLUS D If it s a 4 figure number commencing with 1 then you have a PLUS D with the Version 1 ROM Call MGT on 0792 791100 and we ll arrange a replacement ROM for you GENERAL FEATURES OF Pick POKE It THE NORMAL PLUS D SNAPSHOT FACILITIES Thes operat xactly as befor Press th snapshot button and then select any one of keys I to 5 on the Spectrum If you press the snapshot button menu will appear to Dy saving to disc are retained USE WITH TWO DISC DRIVES the Pick POKE It then key P The menu confirms that if you now press keys 1 the same original PLUS D snapshot facilities for printing and If after moving Into snapshot mode you hold down the CAPS SHIFT key while selecting keys 3 4 or 5 the drive selected will change from one to the other If you have 2 disc drives and wish to use the Pick POKE It facilities on a program contained on a disc which does not then you can force Pick POKE It to take tiles from the alternate disc by holding down CAPS SHIFT while Pick POKE It its you press system files pr E But if you wish to save a file then the destination disc i e th
2. Copyright DRAYSOFT Scanned Typed OCR ed and PDF by Steve Parry Thomas 3 July 2004 This PDF was created to preserve the manual for the future For all ZX Spectrum Plus D And WoS users Thanks to David Russell for the Loan of the original Manual PDF For Michael amp Joshua Hyper links are in the contents so you can jump to the bit you want Pick POKE It from Miles Gordon Technology For use with MGT B PLUS D Interface ZX Spectrum 48K ZX Spectrum ZX Spectrum 128 ZX Spectrum 128K 2 USER MANUAL c Draysoft 1988 NOTICI El The software this manual and the information contained herein is copyright material and may not be reproduced transcribed stored in a retrieval system translated into any language or computer language or transmitted in any form whatsoever without the prior written consent of Miles Gordon Technology The manual is intended to provide the user with detailed information adequate for the efficient installation and operation of the software involved However while every effort has been made to ensure accuracy the writers and the publisher assume no liability resulting from errors in the software or omissions in this manual or from the use of the information contained herein Miles Gordon Technology reserves the right both to change the specifications of the software and to revise this publication from time to time without obligation to notify any person of
3. In the case of PAPEHBOY you d type in 49263 This would bring up this display ENTER NEW VALUE for STRINGS RESTART R EXIT X CONT ENTER Start Address gt 49263 49263 CO6F 61 3D Value gt Columns 1 and 2 display the start address and columns 3 and 4 the current code representation at this address respectively while the right hand column shows the ASCII value To have infinite papers in the game the value you need to type in is 0 Simply type 0 then press ENTER You ll s the amended line displayed 49263 CO6OF 0 00 and the next address 49264 will appear ready for further amendment But you don t want to amend this the next address to change is 50577 So press R then enter to restart When asked for the address type 50577 and do the same as before Continue until you ve made all your changes Finally type X then ENTER to return to the main menu and X again to return to the game All your changes will be retained in RAM and you should now have immunity and infinite lives and papers as you play If you wish to save this version of the game take a snapshot save in the normal way If you d wanted to make a change at address 49265 but not at 49264 above you could have pressed ENTER at 49264 to keep the same lin and pass on directly to the next address You can also use the Edit RAM Contents facility to change an ASCII string for example you might
4. Binary 10 in Decimal is 1010 in Binary 100 is 1100100 and 1000 is 1111101000 Hex numbers ar relatively asy to remember and read particularly where large values are concerned For example the top location in the Spectrum s memory Is 65535 in Decimal but FFFF in Hex When using Pick POKE It you ll see information about addresses In the Spectrum s memory Consider the address as being the place where information is stored rather in the same way that you might put messages into somebody s pigeon hole at work or at school There are 65535 FFFF addresses pigeon holes in the Spectrum s memory and the machine regularly checks each of them to see whether any messages have been left there if it find a message it acts upon it Some of the locations are filled with permanent information for standard control of the computer this is from address 0 to 16384 4000 Then addresses up to 23754 5CCA are taken up by messages affecting for example the screen The remainder of the memory is reserved for messages which determine how a program runs and is the area that we are primarily concerned with when we wish to customise software Many of the addresses may remain empty but where messages are left Pick POKE It will show these as machine code instructions The maximum value of an instruction will be 255 in Decimal or FF If you re a beginner you don t need to understand what the machine code Instruction means I
5. and simply select the pag you require In the Case of the 48K Spectrum selecting any page other than 5 will restore the original RAM contents CALCULATING THE ADDRESS OFFSET If for example you wished to examine or edit the contents of the Spectrum system variable ATTR P the paper and ink colours at address 23693 5CBD it would be necessary to calculate its new location after page 5 has been selected Your calculation would be 23693 16384 49152 56461 Obviously this would be tedious so a special address entry mode is included to enable the program to calculate the address for you The special mode is invoked by placing a symbol before the address i e 23693 or 5CBD The symbol is considered an invalid character when RAM page 5 is not selected RECOMMENDED READING LIST These are books which will help you to learn more about machine code programming Some of them are Spectrum specific others give a more general introduction to the Z80 processor Understanding Your Spectrum lan Logan Melbourne House Mastering Machine Code on your ZX Spectrum Toni Baker Interface The Complete Spectrum ROM Disassembly lan Logan amp Frank O Hara Melbourne House rhe Working Spectrum David Lawrence Sunshine 10 Best Machine Code Routines for the ZX Spectrum John Hardman amp Andrew Hewson Hewson Spectrum 2 Machine Language for the Absolute Beginner Joe Pritchard Melbourne Ho
6. but at the same time relatively easy to read or at least it is if you ve had some practice This language is called machine code Machine code can be represented in either Decimal numbers those that are in everyday use or Hex which stands for Hexadecimal The Hexadecimal system is a way of arranging numbers in units of 16 Q 1 2 3 4 5 6 7 8 9 A B C D E F Conventionally Hex numbers are preceded by the sign Thus 3B equals 59 in Decimal 3 x 16 plus 11 EA equals 234 14 x 16 plus 10 For practice try converting the following Hex numbers to Decimal don t worry you won t have to do this while using Pick POKE It and the answers ar on the last page of this manual 5B E2 20 take care it s not 20 29C BEO 112A 6E1F ABIO FEFF Go on try it before you go on to the next section This will probably seem a strange and unnecessarily complicated method of counting But for the computer engineer or serious programmer it s a better method than Decimal for the following reasons The computer works In a Binary manner remember th lectrical signals that are either on or off There s a direct correlation between Hex and Binary In simple terms the Decimal number 16 is represented by 10 or by 10000 in Binary 256 an important number in computing is represented by 100 or by 100000000 In Binary Conversely there s very little relation between Decimal numbers and
7. key until the required page is flashing then press key X to exit The required page will then be switched in at address 49152 C000 You can then return to the BANK SWITCH program at any time to select another page Note that the page 5 selection is not one of the 128K RAM banks but has a special purpose which is described in the following section There Is no need to restore the original page selection before exiting from Pick POKE It as the exit routine tidies everything for you ii SCREEN AND VARIABLE AREA 48K and 128K Spectrums The memory area from address 16384 4000 to 23754 5CCA contains the screen image channels and Spectrum system variables This area changes as the Pick POKE It programs run To overcome this the original RAM data is saved as a temporary file to the disc and a special facility is provided for looking at this area By using the BANK SWITCH facility and selecting RAM page 5 the temporary tile is loaded in from disc and occupies the address range 49152 C000 to 56522 DCCA where it can be examined and edited without interference The original content of these locations is saved as another temporary file on the disc There is no need to restore the original page selection before exiting from Pick POKE It as the exit routine tidies everything for you If however you wish to restore the original contents at address 49152 C000 then return to the BANK SWITCH program
8. since the area of memory from address 16384 4000 to 23754 5CCA contains the screen image channels and Spectrum system variables this area changes as the Pick POKE It programs run To overcome this the original RAM data is saved as a temporary file on the disc and a special facility is provided for looking at this area This facility is described later in the Bank Switch section If when you are asked for a start address In any of the Pick POKE It programs you simply press ENTER then the default value of 23755 5CCB will be automatically entered because this is where you are likely to want to start However if you have chosen to start with a higher address then the next time you are asked for a start address ENTER will take you to the place wher you started before provided you have not used another of the Pick POKE It programs in the Interim NUMBER ENTRY When you are editing the RAM contents or searching the RAM you will be asked to enter a value as well as specifying an address If you are entering a number which will be a machine code instruction it can b ither a Decimal number or a Hex value in which case you must mark It with a All entries are checked for validity and if necessary an appropriate error message will be displayed and a new value requested You can use the Spectrum s delete key s if you wish to change what you have entered EN
9. such revision or changes CONTENTS INTRODUCTION ad AS A A A AA e e a tae 4 MODTEY ING YOUR SYSTEM DESCS w siteadi See AA a A es 5 What if you can t load Pick POKE Tt L 5 GENERAL FEATURES OF Pick POKE It ooooooooooooooooooo o 6 The Normal PLUS D Snapshot Facilities ____ 06 Use with Two Disc Drives Changing Discs 6 Exiting from Pick POKE It 6 Pick POKE It Temporary Files a ous vac thnttuaidorusccusssldleatelsusbenes 7 Cra SHES ZE n PU arae neh oust NANI M A 7 AN INTRODUCTION TO MACHINE CODE ooooooooooooooooooo o o 8 ENTERING INFORMATION IN Pick POKE It MODE 10 Entering Addresses 10 Default Address Values 10 A A OA 10 A S01 ae ee Oe Oe ine 11 Using a Printer 11 Pick POKE 1t FACILITIES 2 eee eee ee ee AS 12 A E EAN OBS ioc sic ascites ahead A E a eyed 14 Edit RAM Contents 16 Search RAM 18 ADDITIONAL FEATURES FOR PROGRAMMERS o o oooooooooooooooo 20 280 Registers 00 L 20 Binary Number Entry a 2 0 Editing Half of a Register Pair 2 20 o 2 ee as 21 1 Bank Switch 128K Spectrums only 21 2 Screen and Variable Area 48K 128K Spectrum 21 Calculating the Address Offset 22 RECOMMENDED TREADING BEST ii A aed eyes We Seve A Ses 23 ANSWERS TO QUESTIONS ias is a a eee ga al
10. want to change the words HIGH SCORE on screen to BEST SCORE but we ll deal with that in the next section SEARCH RAM This facility allows you to search the contents of RAM for a number or a sequence of numbers or for a string of ASCII values Once you have found what you were looking for you can then choose to disassemble to display memory or to edit memory from that point or to continue the search for the next occurrence Becaus this combines th features of all the Pick POKE It facilities mentioned so far it is likely to be the one you will use most often Suppose you wanted to change the text HIGH SCORE displayed on screen during a game to the text BEST SCORE To try this we took the game BMX RACERS loaded it in the normal way brought up the Pick POKE It main menu and then selected option 9 We started searching from the default value of 23755 Decimal but to make life a little more difficult we started searching not for HIGH SCORE but simply for SCORE To do this entered the value SSCORE Remember that when you type in an ASCII value you need to precede it with S The message STRING FOUND AT 41674 A2CA appeared together with a sub menu 1 DISPLAY MEMORY 2 DISASSEMBLE 3 EDIT MEMORY 4 CONTINUE SEARCH R RESTART SEARCH X QUIT We chose option 1 DISPLAY MEMORY which showed us that the string SCORE did Indeed
11. TERING ASCII VALUES When you are using Pick POKE It s Search and Edit programs you are allowed to look for or replace a string of characters For example you might want to find the part of the program where the instructions to print the High Score table are printed on screen so you d be searching for the character string High Score By convention the letters numbers and sign conventions which appear on the computer keyboard are known as ASCII values In this example when Pick POKE It asks you for the value you re searching for you can type High Score and the appropriate part of the program can be located Whenever you wish to enter an ASCII value simply type and follow it directly with the required text You don t need to type in inverted commas The maximum length of an ASCII string which can be entered at one time is 29 characters not counting the at the start No is required at the end and the string can contain characters if required USING A PRINTER The Disassembler and Display Memory programs can send their output to the printer port using the set up from your original PLUS D system file When you ask the information to be sent to the printer the program will ask for an end address If ENTER alone is pressed then the default value of 65535 FFFF the top of the Spectrum s RAM will be used Printing can be terminated at any time by pressing key X although printing
12. begin at address 41674 But to see whether this was the HIGH SCORE display that we were looking for we needed to go back a few address lines further So we entered R to restart and specified a start address of 41665 Decimal This showed that the ASCII string at this location was only SCORE not HIGH SCORE We entered X which returned us to the sub menu option 4 then continued the search for the next occurrence of the string SCORE This wasn t the one we were looking for either and we had to continue several more times until eventually we found HIGH SCORE beginning at address 44678 T W then selected option 3 from the sub menu EDIT MEMORY In the previous section we described how to change code with the Edit Memory facility but this time we needed to change a string of ASCII values in a sequential sequence of addresses First we typed in the required start address 44978 The address line appeared on the screen with the first letter of the current ASCII string H in the right hand column When asked to enter a value we entered BEST SCORE Immediately th nin dited address lines one address line for the space between th words appeared with all amendments made Having made the change we entered X to return to the sub menu then X again to return to the main Pick POKE It menu then X to return to the original program When we started to edit the program arlier w wer actually looking at a screen wh
13. d PRINT From the ASCII values which follow we can see that this is an interpretation which is likely to be correct the BASIC statement PRINT STOP TAPE makes sense However in a different context 245 Decimal may have another meaning altogether Instructions in the immediate vicinity may have changed the meaning Slightly or completely To draw parallel which may make this Easier to understand the same thing happens in language For Example the word FED has a basic meaning which has something to do with food and eating However in the context I M FED UP it departs from its basic meaning completely although it still looks to be the same word For this reason some of the BASIC command words or ASCII values in column 5 may be an inaccurate interpretation of the code representations in columns 3 or 4 How do you know which are correct and which are not Experience and a little commom sense Patches of column 5 will look like normal lines of BASIC and they Probably are Others won t and they probably aren t However it will make enough sense for you to be able to search for particular areas of the program and well see how to do this in the section on Searching RAM To display the memory select option 7 from the Pick POKE It menu screen Then follow the instructions on pages 9 and 10 to specify addresses and other values EDIT RAM CONTENTS This is the Pick POKE It facility which actually allows you to c
14. e file CHANGING DISCS Once you are in the Pick POKE It Pick POKE It system also containing the Pick POKE It Pick POKE It first If you do the options from the though all is not lost EXITING FROM Pick POKE It When the Pick POKE It menu is Spectrum to return to the means that you can modify a then exit and snapshot save the containing the When you are using any of the special Pick POKE It facilities disc unless you and then Pick POKE It menu have the to disc from the Pick POKE It Menu the must have the Pick POKE It system on it disc on which you are saving mode you should not change the are replacing it with a disc files or unless you exit from try to select another of your Spectrum will crash see below displayed press key X on the normal PLUS D operating system This program in memory using Pick POKE It modified program ona disc not Pick POKE It system files then key X will return you to the main Pick POKE It menu Pick POKE It TEMPORARY FILES When you press the snapshot button and key P you ll hear the disc drive spinning into operation for a few seconds What s happening here is that the software is setting up temporary tiled on disc so that there can be no loss of RAM data while the Pick POKE It facilities are being used These files are given the names DraySoftSC and DraySoftPG Don t give thes file names to an
15. ess ENTER when asked to specify the end address Pick POKE It will default to the top of RAM location 65535 FFFF Then you ll b asked whether you wish to print out the listing If you do press Y if not simply press ENTER For each Instruction to the Z80 processor you ll see the address the bytes forming the instruction and the Mnemonic displayed in a form like this although the actual values will be different when you try it SCCB 00 HOP 5CCC 013700 LD BC 0037 5CCF E7 RST 20 5CDO 310E00 LD SP OOOE 3CD3 00 NOP All the values displayed here are in Hexadecimal although in this display the character is not used As always when you are entering the start address and the end address you can do so in either Decimal or Hex but if you use Hex you must precede the number with The first column shows the address in memory the second column tells you the bytes forming the instruction at this address while the third and fourth columns are a machine code Mnemonic showing the programmer clearly what operation is being performed Newcomers to machine code may be Interested to know what the Mnemonics mean in this example Nop No Operation at this address LD BC 0037 Load the register BC with the value 0037 NB register refers to a location in the computer s CPU It is a location in ROM whereas address refers to a location in memory a locati
16. hange your programs Experienced programmers may want to change ntir screens or perhaps sprites having located them using the Disassembler or the Display Memory facilities But for beginners there s plenty of information in the standard Spectrum magazines to allow you to enter infinite lives or energy or ammunition easily You ll be able to look at all your old games in new ways When starting out try finding a so called Multiface Poke in one of the magazines for a game In your possession Her are a few examples culled from recent magazines PAPERBOY 49263 0 Infinite Papers 50577 190 Infinite Lives 50495 201 Immunity from injury STARGLIDER 54647 201 More fuel 54690 201 More shields BMX KID2 52108 0 Energy LAST NINJA II 29966 n n Lives 40777 0 Lives PLATOON 31138 0 Grenades 31268 0 31269 0 Hits 31270 0 Morale Each of these codes is an address in Decimal then after the comma a machine code Instruction in Decimal to enter at this address If you haven t already done so boot up using your Pick POKE It disc and then load the game in the normal way If the game isn t on the same disc as Pick POKE It it ll make things easier if you save it there Bring up the normal Pick POKE It screen and then select option 4 or 5 as appropriate to resave the game Go back to the Pick POKE It menu screen and select option 8 You ll be asked to specify the start address
17. have meanings close to those in everyday use But while we understand the words they mean nothing to a machine like a computer What the computer CAN understand is whether or not an electrical signal is present whether it is on or off The conventional way to present this information is to use the Binary system Instead of using on or off we use 1 or 0 The Spectrum is an 8 bit computer meaning that eight of these Signals can be sent in parallel to the central processing unit CPU at any one time Thus the signals being sent at any one time could be represented as 01101101 or 0101 101 Did you have to look at these numbers twice to s the differenc between them That s the problem that programmers would face if they had to work in Binary code While the machine understands the signals it would be very difficult to read pages of numbers written in Binary our programs would be filled with errors That s why most people start programming in BASIC which is debatably the easiest of the programming languages When you type LOAD a series of interpretations are made until the CPU receives an electrical signal that it can understand But here s another problem The interpretations take time fractions of a second perhaps but enough to slow down a program appreciably If we had to write our computer games in BASIC they would be very slow moving And so programmers use an intermediate language which ie closer to Binary
18. ich had HIGH SCORE displayed on it When we returned to it the words HIGH SCORE were unchanged this was because Pick POKE It has no effect on the current screen in the computer s memory However as we continued to play the game we saw that HIGH SCORE had indeed been replaced by BEST SCORE We then took an ordinary snapshot save of the program so that on all future occasions we would play it with the same change made If all this is new to you why not experiment by starting with the High Score table in one of your favourite games and altering the names of the highest scorers to your own name Ther are thr things you have to remember First if the high score table uses special graphic characters Instead of the Spectrum s own character set you won t be able to search for an ASCII string as we did in our example so to practise use a game which does use the normal Spectrum characters Secondly if you re replacing a sequence of letters the number of letters you use must be the same as the original Finally when searching for an ASCII string remember that you must use exactly the same letters as the original program if HIGH Score appears on screen then you must search for HIGH Score if it s written HiGh ScOrE that s what you must type This is because the ASCII values for capital letters are different from those for lower case letters ADDITIONAL FEATURES FOR PROGRAMMERS The final two fac
19. ilities on the main Pick POKE It menu Z80 Registers and Bank Switching will be best understood by more xperienced users Z80 REGISTERS When the snapshot button on the PLUS D is pressed the contents of all the 280 registers are stored within the interface so that the program can be correctly restarted Selection of the 280 REGISTERS option from the Pick POKE It menu allows you to display and edit the stored copy of the registers Random changing of the register contents will almost certainly cause the Spectrum to crash or the program in RAM to give strange results Changing the SP Stack Pointer or PC program counter registers will almost certainly have this effect When you exit from the 280 REGISTERS facility you will be asked if you wish to keep the changes you have made If you have made a mistake or are in doubt then answer NO and the original register values will be preserved This facility is avery powerful aid to machine code debugging Since it allows the cause of computer crashes to be explored quite often you will be able to recover the program In addition to the normal Decimal and Hexadecimal modes of number entry this facility allows two other special modes BINARY NUMBER ENTRY Numbers can be entered in Binary form by preceding the entry with B No leading zeros are required EDITING HALF OF A REGISTER PAIR Certain registers in the 280 can be used in pairs f
20. ion to machine code for the novice and is a useful tool even for those who have little interest in programming but who simply wish to breath new lif or Infinite lives into their games By making use of the PLUS D s snapshot button PICK POKE It allows you to inspect edit or print out the contents of RAM while a program is still running This means that you are able to inspect any changes that you may have made immediately by returning to the original program and when you are satisfied with your changes re commence or save the modified program as required And of course the PLUS D will continue to work at Its normal speed loading and saving a full 48K program in less than four seconds achine code la new to you there will be enough guidance in this manual to get you started and to use Pick POKE It properly But if you d like to learn more you ll need to do some extra reading too There s a suggested reading list at the end of the manua artic 1 You ll also find that the various Spectrum magazines print les to introduce their readers to machine code and to suggest how commercial software can be modified with Pokes MODIFYING YOUR SYSTEM DISCS All you need to create your first Pick POKE It system disc is the program supplied on cassette and a PLUS D disc containing a working SYSTEM file This system disc must have at least 48K of free space It s a good idea however to start b
21. ndeed usually sets of instructions act together so a single Instruction may have a different significance at one address when compared with another However as long as you understand what we mean by Hex and Decimal by address and Instruction then you will be able to follow a very simple set of rules to customise your software to give yourself infinite lives or energy ina game or example or perhaps to change the text on the screen If you want to go on to learn more about machine code later all well and good ENTERING INFORMATION IN Pick POKE It MODE ENTERING ADDRESSES When using one of the Pick POKE It facilities you are asked to enter an address and the value can b ntered either as a Decimal number or in Hex For Hexadecimal values the entry must start with a character you don t need to mark Decimal numbers simply nter the number Pick POKE It checks all entries for validity If you ve made an error for example if the number is too low or too high an appropriate error report is given and you are asked to nter the value again If you wish to change your entry use the Spectrum s normal character delete key or keys in the case of the Spectrum 48K DEFAULT ADDRESS VALUES Since the Pick POKE It functions are intended only to be used with RAM the area of memory that changes when programs are running all addresses below 16384 4000 are invalid and cannot be entered Additionally
22. on in RAM RST 20 Restart at Restart Code number 20 LD SP OODE Load the Stack Pointer with the value OODE From this you should be able to see that there s nothing particularly mysterious about Mnemonics although if you want to understand them fully you ll need to do some further reading Note also that not all the possible addresses are listed For example the listing jumps from 5CCC to 5CCF missing out addresses 5CCD and 5CCE In this case this is because the instruction at address 5CCC is executed over thr address lines Experienced programmers will know what they want to do with the Disassembly Newcomers will probably find the other Pick POKE It facilities more useful at first However you might like to experiment by loading a game and printing out the disassembly Or try typing in a short Basic program for xample th Squares program in the PLUS D manual to see what a Basic program looks like in machine code DISPLAY MEMORY This facility displays the Spectrum RAM data either to the screen or the printer A typical display would be arranged like this 23936 5D80 245 F5 PRINT 23937 5D81 34 22 23938 5082 83 53 S 23939 5D83 84 54 T 23940 5D84 79 4F 0 23941 5D85 80 50 P 23942 5086 32 20 23943 5D87 84 54 T 23944 5D88 65 41 A 23945 5D89 80 50 P 23946 5D8A 69 45 E 23947 5D8B 34 22 Column I displays the address number in Decimal Column 2 displays the add
23. or 16 bit values numbers from 0 to 65535 or as two individual registers for 8 bit values numbers from 0 to 255 To allow editing of one half of a register pair without affecting the other the symbols lt and gt can be used The symbol lt is used to change the left hand register and the symbol gt the right hand register The symbol must be the first character in the entry and must precede the B when Binary numbers ar ntered BANK SWITCHING This facility allows you to perform two separate tasks i BANK SELECT 128K Spectrums only The 128K Spectrum RAM consists of 8 separate 16K pages of which only 3 are selected at any one time The RAM pages are numbered 0 to 7 and normally pages 2 and 5 are permanently selected with one of the remaining pages 0 1 3 4 6 or 7 being selected as required RAM page 5 is normally located from address 16384 4000 to 32767 7FFF page 2 is located from address 32768 8000 to 49151 BFFF and one of the remaining six pages occupies the address range 49152 COOO to 65535 FFFF To enable all of the RAM to be accessed by the Pick POKE It routines there needs to be a method of selecting the 6 pages of RAM at address COOO The BANK SWITCHING program provides this facility When the BANK SWITCHING routine is first entered the screen will show the RAM bank which was selected when th PLUS D snapshot button was pressed To select another page simply keep pressing the space
24. ress in Hex Columns 3 and 4 display the RAM data at that address in Decimal and in Hex respectively And column 5 displays the data as an ASCII value where appropriate Let s look at column 5 more closely At address 23936 the code 245 Decimal can be and is in this instance represented in BASIC by the keyword PRINT Similarly the code 34 Decimal at address 23937 has an ASCII value equivalent to and the code 83 Decimal at address 23938 has an ASCII value equivalent to S If you read down the right hand column you ll see that the instructions at this range of addresses is responsible for printing the message STOP TAPE on the screen Notice the consistencies the ASCII value T always has a code representation of 84 Decimal 54 while O has a code representation of 79 Decimal 4F Can you estimate from this information the Decimal and Hex code representations for Q U and G At address 23942 there is no ASCII value marked in our example In fact many addresses will have no information in column 5 or there may be a yellow or white square on the screen If you see a blank yellow square then the ASCII value la a space If you see a blank white or an unmarked square in column 5 then the address contains a machine code instruction or a status value that has nothing to do with an ASCII value There s one small problem In the example above the code 245 Decimal F5 is said to be the equivalent of the BASIC comman
25. s ee 23 Pick INTRODUCTION POKE It adds additional facilities to the PLUS D interface which allow the user to explore and modify existing programs as well BASIC affec Norma of p save all facil can Pick modif their Pick from 128K Of sp If m as providing a very powerful set of tools for machine code and programmers available at the touch of a button without ting the program being worked on lly the PLUS D offers five snapshot facilities two methods rinting screen shots as well as a screen a 49K anda 128K to disc When the PLUS D DOS is modified with Pick POKE It thes features ar retained but there are six extra ities In the first place the contents of the Spectrum RAM be displayed dited searched and disassembled making POKE It an essential tool both for beginners who wish to y their games software and for mor xperienced users writing own programs More advanced users will be able to use POKE It to inspect and edit the 280 registers and to switch one bank of memory to another particularly useful with the Spectrum ecial note are the following Pick POKE It features The software has been professionally designed for ease of operation and clarity of display it is fully menu driven and allows 15 lines of code to be displayed on the screen While experienced programmers will be able to make greatest use of the software Pick POKE It will be an excellent introduct
26. use Z80 and 8080 Assembly Language Programming Kathe Spracklen Hayden Programming the Z780 Rodney Zaks Sybex If your Interest develops and you wish to write your own machine code routines and programs we recommend Hi Soft s Devpak a comprehensive Assembler Debugger with a clear manual Also commended by reviewers recently is Lerm Software s Z80 Toolkit particularly good for writing shorter routines for those who have in understanding of the first principles of machine code programming contact MGT if you need further details Answers to questions on page 8 91 5 x 16 11 242 15 x 16 2 32 668 12 x 16 X 16 9 x 16 12 0056 4394 28191 43792 65535 This number is the highest address in the Spectrum s memory
27. will obviously continue until your printer s buffer is empty Now that you ve learnt the basic principles of Pick POKE It we ll start using the facilities Don t be afraid to experiment If anything goes wrong your original program will still be on disc Remember that you must keep a disc with the Pick POKE It programs in drive 1 when you are using the Pick POKE It programs And if you do get into trouble you can always escape from Pick POKE It and return to the original PLUS D facilities by pressing key X Pick POKE It FACILITIES THE DISASSEMBLER Pick POKE It s Disassembler allows you to display or print out machine code In the Spectrum s RAM together with the Mnemonic For non programmers the Mnemonic is a sort of short hand that programmers use to note the instruction which is actually being given to the CPU If you want to know more you ll need to do some reading any of the books on our recommended reading list will be suitable Typically you ll display or print the disassembly when you want to see a machine code listing of the entire program held in RAM To use the Disassembler press the Snapshot Button then key P to enter the Pick POKE It routines Then press key 6 and you ll be asked to specify the start address If you want to s th ntir program press ENTER and the listing will automatically start from address 23755 5CCB Similarly if you pr
28. y files that you create though we can t imagine why you should want to When you exit from Pick POKE It by pressing key X these temporary files will be automatically erased If the computer crashes while you are using Pick POKE It the temporary file will be retained on the disc so that you can restore it You ll need to boot up the Pick POKE It system again and then follow the instructions in the section on Bank Switching later in this manual In these circumstances the temporary files will be erased automatically for you later you don t need to worry about it Because Pick POKE It writes to your disc you must make sure that your disc is not write protected befor you start work with Pick POKE It CRASHES If your computer crashes while you are using Pick POKE It then you ll need to turn off the electrical power then turn it on again and reboot from scratch The temporary files described above will still remain on disc AN INTRODUCTION TO MACHINE CODE We re not going to attempt to teach machine code here but if you re a newcomer there ar certain principles that you need to understand to mak ffective use of Pick POKE It You ll probably have done at least some elementary programming in BASIC BASIC is a high level computer language high level because it uses terms which are familiar to all of us For example it s easy to understand what LOAD and SAVE mean because these
29. y producing a disc version of the program on cassette and to use this as a master for producing future Pick POKE It system discs To do this you ll require the disc to have at least 80K of free space Start with the PLUS D system booted in the normal way Then with the disc you wish to use in the drive Drive 1 if you have more than one load the program from tape using the command LOAD wee Then simply follow the instructions on screen If you now catalogue your disc you should see three additional files as below DPP1 DPP2 DPP3 Each of these files is about 4K long You will also notice that your original system file has been replaced by one called SYS PP1 If you answered Yes when asked if you wished to save the program on tape onto your disc then two additional tiles will be present PICKPOKEIT POKEITCODE Later you can load the PICKPOKEIT program to create further Pick POKE It system discs without having to use the cassette but keep the tape safe somewhere as a back up From now on if you boot the system using the Pick POKE It system disc the extra facilities will always be available to you although for normal operation the PLUS D will behave as before But when you press the snapshot button and then the Spectrum key P there will be a few seconds of disc activity and then the Pick POKE It menu will be displayed Next we describe how to use the various menu options

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