tristanbgilb wrote: ↑Tue Sep 01, 2020 9:25 pm
Tristan B Gilbert
VB81 Project - ZX81 Emulator Downloadtristanbgilb wrote: ↑Mon Jan 23, 2023 7:08 pm
Introducing the ZX Compiler
Instructions on loading.
Place the cassette on side A, into the recorder. Follow loading instructions, as found in chapter 16 of the ZX81 manual. If at first the program does not load, try different tone and volume levels. If after this it still does not load, try a different tape recorder. There are two copies of ZX COMPILER on the tape. (Use File name "COMPILER")
About the ZX Compiler
The ZX COMPILER is a program, written in basic and machine code that will change a program in "BASIC" into machine code. This can be used to create programs or sub routines that can run up to twenty or thirty times faster than normal 'BASIC'. Because the ZX81 only has a capacity of 16K ram the compiler works in an integer-only, sub-set of BASIC. To save even more space commands have been left out that are not needed, for example REM:- which is not needed in compiled programs anyway and INPUT:- which can be made by a routine using gets and if....then statements. Once your program to be compiled is written, you run the compiler. After a period of fast mode, the program "NEWS" itself and leaves you with a single rem statement containing the machine code (it looks like random junk).
Once written you may either call the code from within a program or directly from the keyboard using LET X=USR 16595.
INSTRUCTIONS ON USE
The program to be compiled is written in 'REM' statements before line 1000 beyond line 1000 is the compiler. The reason for REM's is so you can have extra commands that can't be keyed-in, in normal BASIC. This does mean though that you will have to key in whole commands for example PRINT is P-R-I-N-T. eg:
1 REM PRINT"HELLO"
In the program there are to be no spaces, except in print statements. Also goto statements must be followed by a 'true' line, for example the following will not work.
1 REM PRINT"HELLO"
2 REM GOTO28
When you type run and newline, the screen will blank for a few seconds and then print up:
ERROR IN LINE 28
Which means it can't find any line 28
The compiler program may only have variables A-Z, no strings or arrays. (These maybe be implemented using other commands such as peek and poke).
-Variables in the compiler are not the same ZX81 Variables.
Numbers may be 0-65535. To get a negative number use 65535-x
There may seem a lot you can't do but it is enough to write most programs, (such as space invaders, breakout, etc.) The only way to really find out what the compiler can do is use it, read through the examples and work them out.
In this section I will go through all the commands available on the compiler.
In this section (variable) can mean a number of things:
1) A number 0-65535
2) A letter A-Z
3) RND followed by a variable
4)USR Followed by a variable
6) Deek followed by a variable
7) Peek followed by a variable
eg: RNDA RND200 RNDUSRDEEK16514!!
Top and DEEK need explaining, the others should be clear enough. Top will return the first position on the display that can be poked. It's basic equivalent is : PEEK 16396 + 256 *PEEK 16397 + 1
Deek is the opposite of doke and peeks two locations at the same time. (To return a number 0-65535) Top is the equivalent of DEEK 16396+1. The nascom and other computer use these commands. eg: It can be used for poking a Lazer base with one command.
1 REM DOKE TOP 1153
This can either be followed by text enclosed in speech marks or a variable, (A-Z) it will print the chrs of the variable. The semi colon at the end of the print is automatic. To print at the start of a new line use the following:
1 REM PRINT 118
(Which is the same as the BASIC PRINT CHRS 118) So print can be used in two forms which are:
1. PRINT "--TEXT--"
2. PRINT (VARIABLE)
This is the same as the BASIC INKEY, except only it returns the code (0-128) of the key pressed. It may only be used in one form, if no key is pressed it returns 128.
1. GET (VARIABLE)
eg: 1 REM GET A 2 REM PRINT A 3 REM GOTO 1
It is important that you end a compiler program with either an END if you want execution to stop, or RETURN (see later) if you want to continue the calling BASIC program.
This may only be used in one form:
1) PAUSE (VARIABLE)
It is a delay, the length of which is determined by the (VARIABLE). The longest delay possible would be 65535, it lasts for 2 seconds!!
This is the same as BASIC CLS except it clears all 24 lines of the display, not just 22. It has only one form:
This is the same as the BASIC PRINT AT, except you may "PRINT AT" all 24 lines down. It takes only one form:
1. MOVE (VARIABLE),(VARIABLE)
eg: 1 REM MOVE 23, 10 2 REM PRINT "HELLO" 3 REM END
This is like the BASIC LET statement except you may not have long equations or brackets. It may take only two forms:
1. LET (VARIABLE) = (VARIABLE)
2. LET (VARIABLE) = (OPERATOR) (VARIABLE)
(OPERATOR) can be either +,-,* or /
This is the same as the BASIC SCROLL except that it is a lot quicker and scrolls all 24 lines of the screen.
This is like the BASIC goto except the line number must exist. It may only take one form:
1. GOTO NUMBER (1-999)
This is the same as BASIC GOSUB, except for destination line number which must exist. It can only take one form:
1. GOSUB NUMBER (1-999)
Used in conjunction with GOSUB, this is identical t its BASIC equivalent. Used when not in a GOSUB sub-routine, it will return you to BASIC and continue with the calling program. It may only take one form:
This is the same as BASIC PLOT. It may take only one form:
1. PLOT (VARIABLE), (VARIABLE)
This is the same as BASIC UNPLOT. It may take only one form:
1. UNPLOT (VARIABLE),(VARIABLE)
This is the same as its BASIC equivalent. It may only take one form:
1. POKE (VARIABLE),(VARIABLE)
Is used on the nascom and other computer, it pokes two locations at the same time with a number of up to 65535. The low byte of the number at the address and the high byte at address +1. For more information see example programs. It can only take one form:
1. DOKE (VARIABLE),(VARIABLE)
IF is used in only one way:
1. IF (VARIABLE) (SIGN)(VARIABLE)______
(SIGN) can mean either =,<>,<>. There is no need to use the then statement. For more information see example programs.
eg: IF A>2 GOTO 10
These are all the commands allowed in the compiler. But as you can see from the example programs, these are enough.
This program will invert the screen, then Return to basic not stop. It will invert all 24 lines of the display.
1 REM LETB=24
2 REM LETA=TOP
3 REM IFPEEKA=118GOTO10
4 REM LETZ=PEEKA+128 : NUMBER OF LINES
5 REM POKEA,Z : TOP OF SCREEN
6 REM LETA=A+1 : END OF LINE ?
7 REM GOTO3 : INVERT IT
10 REM LET B=B-1
11 REM IFB=0RETURN : "RETURN" TO BASIC, USE END
12 REM GOTO6 STOP WITH AN ERROR CODE:
Try this program out, then try it in BASIC to see how slow it is.
This program demonstrates the DEEK and DOKE commands, DOKE is used to 'save' the variable while it is used for something else, DEEK reads it back again.
1 REM LETA=45192
2 REM DOKE30000,A
3 REM LETA=0
4 REM LETA=DEEK30000
5 REM IFA<>45192PRINT"THIS WILL NEVER BE PRINTED"
6 REM END
In this program location 30000 was chosen because it is high up in the memory and will not interfere with anything.
WHEN YOU HAVE WRITTEN A PROGRAM
When you have written your program in REM statements, SAVE a copy on cassette (in case you have to de-bug it) Then RUN, this will run the compiler as it will go past REMS. After a delay (10mins for 4k program0 the screen will return. If it says error, correct error and re-run it. If it comes up with one rem followed by junk then it has finished compiling, BEFORE YOU DO ANYTHING ELSE type in: 2 RAND USR 16595
Then SAVE another copy of the program and run it. If the program does something odd, try and see what is happening, re-load the first copy and correct the program.
Don't forget in machine code there is no 'break' key to test for one use.
1. REM GETA
2. REM IFA=0END
Even a one line compiler program when compiled may seem to take up a lot of room, this is quite normal because about 1K is taken up with variables and routines. The compiler was really developed for small fast routines to be used in a BASIC program or entire games in machine code.
If you want to interchange basic variables and compiler variables, the compiler variables are held at 16514 low byte first, high byte next. A(low) is at 16514, B(low) is at 16515 and so on.
In the program you will see two sets of inverse AJGs this is so the author can identify any compiled program. (No program may be used personal gain which in any way connected with the compiler without the permission of the author.
Try to use POKE and PEEK, (deeks and dokes) more as they are very fast in the compiler. Things like PRINT, PRINT AT, PLOT, UNPLOT use basic routines to space so they will only be executed at about twice the speed as normal.
The RND function is not very random when displaying the results, but it is good enough for normal random decisions. (This is again due to the lack of space available). Compilers available for other computers may need 4K of code for one line of compiled program!!
1) Add all the numbers 1-1000 together.
(returns the answer in s 165114+16515)
1 REM LETA=0
2 REM LETC=0
3 REM LETA=A+C
4 REM LETC=C+1
5 REM IFC 101 GOTO3
6 REM END
Type this in, then RUN it, to see the answer
PRINT PEEK 16514+256*PEEK 16515
try out he program in BASIC as well and see the difference in speed
1 REM LET P=0
2 REM MOVE23,P
3 REM PRINT34
4 REM GET A
5 REM IFA=33LETp=p-1 key 5
6 REM IFA=36LETp=P+1 key 8
7 REM IFP=65535LETP=0
8 REM IFP=31LETp=30
9 REM SCROLL
10 REM GOTO2
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