.
CP/M Squares
by Rick Kephart January 27, 1988
Not wanting to let the Z80 (CP/M) microprocessor in my Commodore-128 go
to waste, I wanted to write some programs for it just so it could be put
to use. I did pay for it, after all. This program can be loaded and
played using nothing more than the CP/M system disk already supplied with
the C-128.
This is a guessing game. The program picks a random square on a
checkerboard which you must locate. Enter a row and column as a letter
and a number (i.e. the upper left-hand corner square is 'a1' and the lower
right-hand corner square is 'h8') and press RETURN, and you will be told
if the correct square is above, below, left, or right of that guess. Your
guesses will be counted until the correct square is located, at which
point you will be prompted to play again, or quit back to CP/M.
Note that though the program is written in Z80 machine language, the
program listed here is in C-128 BASIC! This program will produce the
machine-language code which the other microprocessor will eventually use,
POKEing it into memory. But to use it, it must first be written to a
CP/M-formatted disk, which the BASIC SAVE command cannot do. So how do we
get the program onto a disk?
This is not as difficult as you might imagine. There is a handy
program on side 2 of the CP/M system disk which is just what we need: it
saves any section of memory onto a CP/M disk.
The Z80 microprocessor uses BANK1 memory. This is the BANK of memory
which will be visible in CP/M mode. Most of this memory remains intact
when you BOOT the CP/M disk. So all that needs to be done to transfer our
program to a CP/M disk is to POKE it into any safe section of BANK1 memory
(here we'll start at 1000 hex or 4096 decimal). BANK1 is used for BASIC
variables, but this program uses so few variables they won't even come
close to this location, but since it's always good practice to change some
the variable-pointers so that the variables cannot overwrite the data,
we'll do that here anyway.
As soon as the program has POKEd the ML data into memory, you are
prompted to insert side 1 of the CP/M system disk, and the program will
BOOT it, to put you into CP/M mode.
Now you are in CP/M mode, with a Z80 game in memory.
Load the SAVE.COM program on side 2 of the system disk with this at the
"A>" prompt:
A>save
A>save
(Note that you type this in twice to start the program). You will be
prompted to enter a filename. You may use any name for it, but you must
end it with .COM or you won't be able to load and run it.
You will then be prompted for a start address and ending address. The
start address, as you might have expected, is 1000. The ending address is
12B3. Here is what it would all look like if you name the program
"SQUARES.COM"
CP/M 3 SAVE Version 3.0
Enter file (type RETURN to exit): squares.com
Beginning hex address 1000
Ending hex address 12b3
Once this has all been done, the program is ready to play! Just enter
your filename at the prompt:
A>squares
And the program will load and run!
I wrote this program without spending any money on CP/M. I used two
books I got from a local library to learn to program the chip: "Soul of
CP/M" by Michael Waite & Robert Lafore (Howard W. Sams & Co., Inc., 1983),
which explains simply and clearly how to program in CP/M, and "A Practical
Guide to CP/M" by Carl Townsend (dilithium Press, 1983), which has some
very useful charts (including all the opcodes for the mnemonics).
Unfortunately, both books only describe 8080 commands, but they were
sufficient to write this game.
Not having any assembler, the source code was assembled by hand, and
then the machine-language program typed in using the C-128 built-in
monitor, and saved using the SAVE.COM program on the CP/M system disk. It
was then disassembled using a public-domain Z80 disassembler which I got
from a local CP/M BBS.
10 POKE 58,16: CLR: BANK 1: PRINT "READING DATA": FOR I = 4096 TO 4787:
READ A: X=X+A: POKE I,A: NEXT: IF X<>45177 THEN PRINT "ERROR IN DATA
STATEMENTS": END
20 PRINT "INSERT CP/M SYSTEM DISK": PRINT "PRESS ANY KEY WHEN READY"
30 PRINT "THEN RUN SAVE AND USE 1000 FOR THE BEGINNING ADDRESS":
PRINT "AND 12B3 FOR THE ENDING
ADDRESS": GETKEY A$: BOOT
100 DATA 17,47,2,14,9,205,5,0,62,1,50,0,6,197,14,11,205,5,0,183,194,
31,1,193,121,128,79,4,195,13,1,193
110 DATA 120,230,7,50,0,4,121,230,7,50,1,4,17,254,4,62,2,18,14,10,205,
5,0,30,10,14,2,205,5,0,58,0
120 DATA 4,71,58,0,5,214,97,184,202,94,1,17,230,1,210,84,1,17,235,1,
14,9,205,5,0,62,0,50,254,4,58,1
130 DATA 4,71,58,1,5,214,49,184,202,204,1,245,58,254,4,183,194,123,
1,17,242,1,14,9,205,5,0,241,17,246,1,210
140 DATA 133,1,17,252,1,14,9,205,5,0,58,0,6,60,50,0,6,254,65,218,151,
1,201,17,3,2,14,9,205,5,0,6
150 DATA 0,58,0,6,254,10,218,175,1,214,10,4,195,164,1,245,120,198,48,
95,14,2,205,5,0,241,198,48,95,14,2,205
160 DATA 5,0,30,58,14,2,205,5,0,195,44,1,58,254,4,183,202,138,1,17,13,
2,14,9,205,5,0,14,1,205,5,0
170 DATA 254,121,202,0,1,201,32,85,112,32,36,32,68,111,119,110,32,36,97,
110,100,36,32,76,101,102,116,36,32,82,105,103
180 DATA 104,116,36,13,10,71,117,101,115,115,32,35,36,13,10,7,84,104,97,
116,39,115,32,105,116,33,13,10,10,80,108,97
190 DATA 121,32,97,103,97,105,110,63,40,121,92,110,41,7,36,13,10,10,9,
32,32,49,32,50,32,51,32,52,32,53,32,54
200 DATA 32,55,32,56,13,10,9,97,124,35,32,35,32,35,32,35,32,35,32,35,32,
35,32,35,124,13,10,9,98,124,32,35
210 DATA 32,35,32,35,32,35,32,35,32,35,32,35,32,124,13,10,9,99,124,35,32,
35,32,35,32,35,32,35,32,35,32,35
220 DATA 32,35,124,13,10,9,100,124,32,35,32,35,32,35,32,35,32,35,32,35,
32,35,32,124,13,10,9,101,124,35,32,35
230 DATA 32,35,32,35,32,35,32,35,32,35,32,35,124,13,10,9,102,124,32,35,
32,35,32,35,32,35,32,35,32,35,32,35
240 DATA 32,124,13,10,9,103,124,35,32,35,32,35,32,35,32,35,32,35,32,35,
32,35,124,13,10,9,104,124,32,35,32,35
250 DATA 32,35,32,35,32,35,32,35,32,35,32,124,13,10,9,32,67,80,47,77,32,
83,81,85,65,82,69,83,32,70,79,82
260 DATA 13,10,32,32,32,32,32,32,32,32,32,32,32,32,84,72,69,32,67,45,49,
50,56,13,10,10,7,71,117,101,115,115
270 DATA 32,97,32,82,111,119,32,40,108,111,119,101,114,45,99,97,115,101,
32,108,101,116,116,101,114,41,32,102,111,108,108,111
280 DATA 119,101,100,32,98,121,32,97,32,99,111,108,117,109,110,32,40,110,
117,109,98,101,114,41,32,97,110,100,32,121,111,117
290 DATA 39,108,108,32,98,101,32,116,111,108,100,32,105,102,32,116,104,
101,32,67,80,47,77,32,83,81,85,65,82,69,32,105
300 DATA 115,32,85,112,44,32,68,111,119,110,44,32,76,101,102,116,44,32,
111,114,32,82,105,103,104,116,32,102,114,111,109,32
310 DATA 116,104,101,114,101,46,13,10,10,71,117,101,115,115,32,35,48,
49,58,36
____________________________________________________________________
ORG 0100H
BDOS EQU 05H
BUFFER EQU 04FEH
COUNT EQU 0600H
GUESSCOLUMN EQU 0501H
GUESSROW EQU 0500H
RANDOMCOLUMN EQU 0401H
RANDOMROW EQU 0400H
BEGIN:
LD DE,INTROMESSAGE
LD C,9 ;print-string: LoaD register C
CALL BDOS ; with 9 and Call (JSR) to BDOS
LD A,1
LD (COUNT),A ;keep track of # of guesses
; starting with A=1
WAIT:
PUSH BC ;BC will hold 2 Rnd numbers
LD C,0BH ;get console status (H=Hex)
CALL BDOS ; -checks for key-press-
OR A
JP NZ,CONT ;Zero-flag set=key-press
; and break out of WAIT: loop
POP BC ;random numbers in B and C
LD A,C
ADD A,B ;randomizes number in C
LD C,A
INC B ;randomizes number in B
JP WAIT ; Loop back to WAIT:
CONT:
POP BC ;Pop random numbers
LD A,B ;get 1st rnd number into A
AND 7 ;must be less than 8
LD (RANDOMROW),A ;store number in memory
LD A,C ;repeat for second number
AND 7
LD (RANDOMCOLUMN),A
GETGUESS:
LD DE,BUFFER ;prepare buffer for input
LD A,2 ;admit two characters
LD (DE),A
LD C,0AH ;read console buffer by putting
CALL BDOS ; 10 ($0A) in register C
LD E,0AH ;print line-feed
LD C,2 ;console output
CALL BDOS
LD A,(RANDOMROW) ;check row guess (letter)
LD B,A ;put correct row in B
LD A,(GUESSROW)
SUB 61H ;ASCII-letter to number 0-7
CP B
JP Z,CHECKCOLUMN ;zero-flag-set=correct row
LD DE,UPMESSAGE
JP NC,PRINT1 ;Carry-clear=too high
LD DE,DOWNMESSAGE
PRINT1:
LD C,9 ;print whichever string
CALL BDOS ; was put in DE
LD A,0 ;set flag to indicate
LD (BUFFER),A ; wrong row was guessed
CHECKCOLUMN:
LD A,(RANDOMCOLUMN) ;get true column
LD B,A ; and put it in B
LD A,(GUESSCOLUMN)
SUB '1' ;ASCII-number to number 0-7
CP B
JP Z,RIGHTCOLUMN ;zero-flag-set=correct col.
PUSH AF ;push status word
LD A,(BUFFER) ;correct-row flag
OR A
JP NZ,NOAND ;don't print "and" if no
LD DE,ANDMESSAGE ; row direction was printed
LD C,9 ;print-string
CALL BDOS
NOAND:
POP AF ;get flags back
LD DE,LEFTMESSAGE
JP NC,PRINT2 ;Carry-clear=too high
LD DE,RIGHTMESSAGE
PRINT2:
LD C,9 ;print whichever string is in DE
CALL BDOS
COUNTER:
LD A,(COUNT) ;current number of guesses
INC A ;update number of guesses
LD (COUNT),A ;store latest # of guesses
CP 40H ;maximum guesses=64
JP C,DECIMAL
RET
DECIMAL:
LD DE,GUESSMESSAGE
LD C,9 ;print-string
CALL BDOS
LD B,0 ;B holds number of tens
LD A,(COUNT) ;number to print as decimal
SUBTRACTIONS:
CP 0AH
JP C,PRINTTENS ;now less than 10
SUB 0AH
INC B ;count number of tens
JP SUBTRACTIONS
PRINTTENS:
PUSH AF ;store units digit
LD A,B ;get tens digit
ADD A,'0' ;convert to ASCII numeral
LD E,A ;print it
LD C,2 ;console output
CALL BDOS
POP AF ;get units
ADD A,'0' ;convert to ASCII
LD E,A ;print it
LD C,2 ;console output
CALL BDOS
LD E,':' ;print a colon
LD C,2 ;console output
CALL BDOS
JP GETGUESS ;get next guess
RIGHTCOLUMN:
LD A,(BUFFER) ;correct-row flag
OR A
JP Z,COUNTER ;zero=wrong row
LD DE,CORRECTMESSA
LD C,9 ;print-string
CALL BDOS
LD C,1 ;console input
CALL BDOS
CP 'y'
JP Z,BEGIN ;if input="y" play again
RET
UPMESSAGE:
DB ' Up $' ; $ means the end-of-string
DOWNMESSAGE:
DB ' Down $'
ANDMESSAGE:
DB 'and$'
LEFTMESSAGE:
DB ' Left$'
RIGHTMESSAGE:
DB ' Right$'
GUESSMESSAGE:
DB 0DH,0AH,'Guess #$'
CORRECTMESSA:
DB 0DH,0AH,07H,'That's it!'
DB 0DH,0AH,0AH,'Play again?(y',5CH,'n)',07H,'$'
INTROMESSAGE:
DB 0DH,0AH,0AH,09H,' 1 2 3 4 5 6 7 8',0DH,0AH,09H
DB 'a',7CH,'# # # # # # # #',7CH,0DH,0AH,09H
DB 'b',7CH,' # # # # # # # ',7CH,0DH,0AH,09H
DB 'c',7CH,'# # # # # # # #',7CH,0DH,0AH,09H
DB 'd',7CH,' # # # # # # # ',7CH,0DH,0AH,09H
DB 'e',7CH,'# # # # # # # #',7CH,0DH,0AH,09H
DB 'f',7CH,' # # # # # # # ',7CH,0DH,0AH,09H
DB 'g',7CH,'# # # # # # # #',7CH,0DH,0AH,09H
DB 'h',7CH,' # # # # # # # ',7CH,0DH,0AH,09H
DB ' CP/M SQUARES FOR',0DH,0AH
DB ' THE C-128',0DH,0AH,0AH,07H
DB 'Guess a Row (lower-case letter) '
DB 'followed by a column (number) and you'll '
DB 'be told if the CP/M SQUARE is Up, Down, '
DB 'Left, or Right from there.',0DH,0AH,0AH
DB 'Guess #01:$'
END
You can write to me at .
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