MicroChess by Peter Jennings, modified by Daryl Rictor.
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MicroChess is a very famous game written by Peter Jennings in 1976. It was originally written for the MOS Technology KIM-1 but is easily ported and was used on other systems like the Rockwell AIM-65.
UCHESS.PDF (884k) - The original version can be downloaded here in Portable Document Format. It was provided by Cameron Kaiser's Secret Weapons of Commodore website. The original author, Peter Jennings, has given 6502.org permission to post it here.
UCHESS2.TXT (21k) - Daryl Rictor has adapted the program for use on computers with a 6551-based serial port, which is shown in the screenshot above. This new version may be downloaded here and is also presented below.
;***********************************************************************
;
; MicroChess (c) 1996-2002 Peter Jennings, peterj@benlo.com
;
;***********************************************************************
; I have been given permission to distribute this program by the
; author and copyright holder, Peter Jennings. Please get his
; permission if you wish to re-distribute a modified copy of
; this file to others. He specifically requested that his
; copyright notice be included in the source and binary images.
; Thanks!
;
; modified by Daryl Rictor to work over a serial terminal connection, August 2002.
;
; 6551 I/O Port Addresses
;
ACIADat = $7F70
ACIASta = $7F71
ACIACmd = $7F72
ACIACtl = $7F73
;
; page zero variables
;
BOARD = $50
BK = $60
PIECE = $B0
SQUARE = $B1
SP2 = $B2
SP1 = $B3
INCHEK = $B4
STATE = $B5
MOVEN = $B6
REV = $B7
OMOVE = $DC
WCAP0 = $DD
COUNT = $DE
BCAP2 = $DE
WCAP2 = $DF
BCAP1 = $E0
WCAP1 = $E1
BCAP0 = $E2
MOB = $E3
MAXC = $E4
CC = $E5
PCAP = $E6
BMOB = $E3
BMAXC = $E4
BMCC = $E5 ; was BCC (TASS doesn't like it as a label)
BMAXP = $E6
XMAXC = $E8
WMOB = $EB
WMAXC = $EC
WCC = $ED
WMAXP = $EE
PMOB = $EF
PMAXC = $F0
PCC = $F1
PCP = $F2
OLDKY = $F3
BESTP = $FB
BESTV = $FA
BESTM = $F9
DIS1 = $FB
DIS2 = $FA
DIS3 = $F9
temp = $FC
;
;
;
*=$1000 ; load into RAM @ $1000-$15FF
LDA #$00 ; REVERSE TOGGLE
STA REV
JSR Init_6551
CHESS CLD ; INITIALIZE
LDX #$FF ; TWO STACKS
TXS
LDX #$C8
STX SP2
;
; ROUTINES TO LIGHT LED
; DISPLAY AND GET KEY
; FROM KEYBOARD
;
OUT JSR pout ; DISPLAY AND
JSR KIN ; GET INPUT *** my routine waits for a keypress
; CMP OLDKY ; KEY IN ACC *** no need to debounce
; BEQ OUT ; (DEBOUNCE)
; STA OLDKY
;
CMP #$43 ; [C]
BNE NOSET ; SET UP
LDX #$1F ; BOARD
WHSET LDA SETW,X ; FROM
STA BOARD,X ; SETW
DEX
BPL WHSET
LDX #$1B ; *ADDED
STX OMOVE ; INITS TO $FF
LDA #$CC ; Display CCC
BNE CLDSP
;
NOSET CMP #$45 ; [E]
BNE NOREV ; REVERSE
JSR REVERSE ; BOARD IS
SEC
LDA #$01
SBC REV
STA REV ; TOGGLE REV FLAG
LDA #$EE ; IS
BNE CLDSP
;
NOREV CMP #$40 ; [P]
BNE NOGO ; PLAY CHESS
JSR GO
CLDSP STA DIS1 ; DISPLAY
STA DIS2 ; ACROSS
STA DIS3 ; DISPLAY
BNE CHESS
;
NOGO CMP #$0D ; [Enter]
BNE NOMV ; MOVE MAN
JSR MOVE ; AS ENTERED
JMP DISP
NOMV CMP #$41 ; [Q] ***Added to allow game exit***
BEQ DONE ; quit the game, exit back to system.
JMP INPUT ; process move
DONE JMP $FF00 ; *** MUST set this to YOUR OS starting address
;
; THE ROUTINE JANUS DIRECTS THE
; ANALYSIS BY DETERMINING WHAT
; SHOULD OCCUR AFTER EACH MOVE
; GENERATED BY GNM
;
;
;
JANUS LDX STATE
BMI NOCOUNT
;
; THIS ROUTINE COUNTS OCCURRENCES
; IT DEPENDS UPON STATE TO INDEX
; THE CORRECT COUNTERS
;
COUNTS LDA PIECE
BEQ OVER ; IF STATE=8
CPX #$08 ; DO NOT COUNT
BNE OVER ; BLK MAX CAP
CMP BMAXP ; MOVES FOR
BEQ XRT ; WHITE
;
OVER INC MOB,X ; MOBILITY
CMP #$01 ; + QUEEN
BNE NOQ ; FOR TWO
INC MOB,X
;
NOQ BVC NOCAP
LDY #$0F ; CALCULATE
LDA SQUARE ; POINTS
ELOOP CMP BK,Y ; CAPTURED
BEQ FOUN ; BY THIS
DEY ; MOVE
BPL ELOOP
FOUN LDA POINTS,Y
CMP MAXC,X
BCC LESS ; SAVE IF
STY PCAP,X ; BEST THIS
STA MAXC,X ; STATE
;
LESS CLC
PHP ; ADD TO
ADC CC,X ; CAPTURE
STA CC,X ; COUNTS
PLP
;
NOCAP CPX #$04
BEQ ON4
BMI TREE ;(=00 ONLY)
XRT RTS
;
; GENERATE FURTHER MOVES FOR COUNT
; AND ANALYSIS
;
ON4 LDA XMAXC ; SAVE ACTUAL
STA WCAP0 ; CAPTURE
LDA #$00 ; STATE=0
STA STATE
JSR MOVE ; GENERATE
JSR REVERSE ; IMMEDIATE
JSR GNMZ ; REPLY MOVES
JSR REVERSE
;
LDA #$08 ; STATE=8
STA STATE ; GENERATE
; JSR OHM ; CONTINUATION
JSR UMOVE ; MOVES
;
JMP STRATGY ; FINAL EVALUATION
NOCOUNT CPX #$F9
BNE TREE
;
; DETERMINE IF THE KING CAN BE
; TAKEN, USED BY CHKCHK
;
LDA BK ; IS KING
CMP SQUARE ; IN CHECK?
BNE RETJ ; SET INCHEK=0
LDA #$00 ; IF IT IS
STA INCHEK
RETJ RTS
;
; IF A PIECE HAS BEEN CAPTURED BY
; A TRIAL MOVE, GENERATE REPLIES &
; EVALUATE THE EXCHANGE GAIN/LOSS
;
TREE BVC RETJ ; NO CAP
LDY #$07 ; (PIECES)
LDA SQUARE
LOOPX CMP BK,Y
BEQ FOUNX
DEY
BEQ RETJ ; (KING)
BPL LOOPX ; SAVE
FOUNX LDA POINTS,Y ; BEST CAP
CMP BCAP0,X ; AT THIS
BCC NOMAX ; LEVEL
STA BCAP0,X
NOMAX DEC STATE
LDA #$FB ; IF STATE=FB
CMP STATE ; TIME TO TURN
BEQ UPTREE ; AROUND
JSR GENRM ; GENERATE FURTHER
UPTREE INC STATE ; CAPTURES
RTS
;
; THE PLAYER'S MOVE IS INPUT
;
INPUT CMP #$08 ; NOT A LEGAL
BCS ERROR ; SQUARE #
JSR DISMV
DISP LDX #$1F
SEARCH LDA BOARD,X
CMP DIS2
BEQ HERE ; DISPLAY
DEX ; PIECE AT
BPL SEARCH ; FROM
HERE STX DIS1 ; SQUARE
STX PIECE
ERROR JMP CHESS
;
; GENERATE ALL MOVES FOR ONE
; SIDE, CALL JANUS AFTER EACH
; ONE FOR NEXT STE?
;
;
GNMZ LDX #$10 ; CLEAR
GNMX LDA #$00 ; COUNTERS
CLEAR STA COUNT,X
DEX
BPL CLEAR
;
GNM LDA #$10 ; SET UP
STA PIECE ; PIECE
NEWP DEC PIECE ; NEW PIECE
BPL NEX ; ALL DONE?
RTS ; #NAME?
;
NEX JSR RESET ; READY
LDY PIECE ; GET PIECE
LDX #$08
STX MOVEN ; COMMON START
CPY #$08 ; WHAT IS IT?
BPL PAWN ; PAWN
CPY #$06
BPL KNIGHT ; KNIGHT
CPY #$04
BPL BISHOP ; BISHOP
CPY #$01
BEQ QUEEN ; QUEEN
BPL ROOK ; ROOK
;
KING JSR SNGMV ; MUST BE KING!
BNE KING ; MOVES
BEQ NEWP ; 8 TO 1
QUEEN JSR LINE
BNE QUEEN ; MOVES
BEQ NEWP ; 8 TO 1
;
ROOK LDX #$04
STX MOVEN ; MOVES
AGNR JSR LINE ; 4 TO 1
BNE AGNR
BEQ NEWP
;
BISHOP JSR LINE
LDA MOVEN ; MOVES
CMP #$04 ; 8 TO 5
BNE BISHOP
BEQ NEWP
;
KNIGHT LDX #$10
STX MOVEN ; MOVES
AGNN JSR SNGMV ; 16 TO 9
LDA MOVEN
CMP #$08
BNE AGNN
BEQ NEWP
;
PAWN LDX #$06
STX MOVEN
P1 JSR CMOVE ; RIGHT CAP?
BVC P2
BMI P2
JSR JANUS ; YES
P2 JSR RESET
DEC MOVEN ; LEFT CAP?
LDA MOVEN
CMP #$05
BEQ P1
P3 JSR CMOVE ; AHEAD
BVS NEWP ; ILLEGAL
BMI NEWP
JSR JANUS
LDA SQUARE ; GETS TO
AND #$F0 ; 3RD RANK?
CMP #$20
BEQ P3 ; DO DOUBLE
JMP NEWP
;
; CALCULATE SINGLE STEP MOVES
; FOR K,N
;
SNGMV JSR CMOVE ; CALC MOVE
BMI ILL1 ; -IF LEGAL
JSR JANUS ; -EVALUATE
ILL1 JSR RESET
DEC MOVEN
RTS
;
; CALCULATE ALL MOVES DOWN A
; STRAIGHT LINE FOR Q,B,R
;
LINE JSR CMOVE ; CALC MOVE
BCC OVL ; NO CHK
BVC LINE ; NOCAP
OVL BMI ILL ; RETURN
PHP
JSR JANUS ; EVALUATE POSN
PLP
BVC LINE ; NOT A CAP
ILL JSR RESET ; LINE STOPPED
DEC MOVEN ; NEXT DIR
RTS
;
; EXCHANGE SIDES FOR REPLY
; ANALYSIS
;
REVERSE LDX #$0F
ETC SEC
LDY BK,X ; SUBTRACT
LDA #$77 ; POSITION
SBC BOARD,X ; FROM 77
STA BK,X
STY BOARD,X ; AND
SEC
LDA #$77 ; EXCHANGE
SBC BOARD,X ; PIECES
STA BOARD,X
DEX
BPL ETC
RTS
;
; CMOVE CALCULATES THE TO SQUARE
; USING SQUARE AND THE MOVE
; TABLE FLAGS SET AS FOLLOWS:
; N#NAME? MOVE
; V#NAME? (LEGAL UNLESS IN CR)
; C#NAME? BECAUSE OF CHECK
; [MY &THANKS TO JIM BUTTERFIELD
; WHO WROTE THIS MORE EFFICIENT
; VERSION OF CMOVE)
;
CMOVE LDA SQUARE ; GET SQUARE
LDX MOVEN ; MOVE POINTER
CLC
ADC MOVEX,X ; MOVE LIST
STA SQUARE ; NEW POS'N
AND #$88
BNE ILLEGAL ; OFF BOARD
LDA SQUARE
;
LDX #$20
LOOP DEX ; IS TO
BMI NO ; SQUARE
CMP BOARD,X ; OCCUPIED?
BNE LOOP
;
CPX #$10 ; BY SELF?
BMI ILLEGAL
;
LDA #$7F ; MUST BE CAP!
ADC #$01 ; SET V FLAG
BVS SPX ; (JMP)
;
NO CLV ; NO CAPTURE
;
SPX LDA STATE ; SHOULD WE
BMI RETL ; DO THE
CMP #$08 ; CHECK CHECK?
BPL RETL
;
; CHKCHK REVERSES SIDES
; AND LOOKS FOR A KING
; CAPTURE TO INDICATE
; ILLEGAL MOVE BECAUSE OF
; CHECK SINCE THIS IS
; TIME CONSUMING, IT IS NOT
; ALWAYS DONE
;
CHKCHK PHA ; STATE #392
PHP
LDA #$F9
STA STATE ; GENERATE
STA INCHEK ; ALL REPLY
JSR MOVE ; MOVES TO
JSR REVERSE ; SEE IF KING
JSR GNM ; IS IN
JSR RUM ; CHECK
PLP
PLA
STA STATE
LDA INCHEK
BMI RETL ; NO - SAFE
SEC ; YES - IN CHK
LDA #$FF
RTS
;
RETL CLC ; LEGAL
LDA #$00 ; RETURN
RTS
;
ILLEGAL LDA #$FF
CLC ; ILLEGAL
CLV ; RETURN
RTS
;
; REPLACE PIECE ON CORRECT SQUARE
;
RESET LDX PIECE ; GET LOGAT
LDA BOARD,X ; FOR PIECE
STA SQUARE ; FROM BOARD
RTS
;
;
;
GENRM JSR MOVE ; MAKE MOVE
GENR2 JSR REVERSE ; REVERSE BOARD
JSR GNM ; GENERATE MOVES
RUM JSR REVERSE ; REVERSE BACK
;
; ROUTINE TO UNMAKE A MOVE MADE BY
; MOVE
;
UMOVE TSX ; UNMAKE MOVE
STX SP1
LDX SP2 ; EXCHANGE
TXS ; STACKS
PLA ; MOVEN
STA MOVEN
PLA ; CAPTURED
STA PIECE ; PIECE
TAX
PLA ; FROM SQUARE
STA BOARD,X
PLA ; PIECE
TAX
PLA ; TO SOUARE
STA SQUARE
STA BOARD,X
JMP STRV
;
; THIS ROUTINE MOVES PIECE
; TO SQUARE, PARAMETERS
; ARE SAVED IN A STACK TO UNMAKE
; THE MOVE LATER
;
MOVE TSX
STX SP1 ; SWITCH
LDX SP2 ; STACKS
TXS
LDA SQUARE
PHA ; TO SQUARE
TAY
LDX #$1F
CHECK CMP BOARD,X ; CHECK FOR
BEQ TAKE ; CAPTURE
DEX
BPL CHECK
TAKE LDA #$CC
STA BOARD,X
TXA ; CAPTURED
PHA ; PIECE
LDX PIECE
LDA BOARD,X
STY BOARD,X ; FROM
PHA ; SQUARE
TXA
PHA ; PIECE
LDA MOVEN
PHA ; MOVEN
STRV TSX
STX SP2 ; SWITCH
LDX SP1 ; STACKS
TXS ; BACK
RTS
;
; CONTINUATION OF SUB STRATGY
; -CHECKS FOR CHECK OR CHECKMATE
; AND ASSIGNS VALUE TO MOVE
;
CKMATE LDY BMAXC ; CAN BLK CAP
CPX POINTS ; MY KING?
BNE NOCHEK
LDA #$00 ; GULP!
BEQ RETV ; DUMB MOVE!
;
NOCHEK LDX BMOB ; IS BLACK
BNE RETV ; UNABLE TO
LDX WMAXP ; MOVE AND
BNE RETV ; KING IN CH?
LDA #$FF ; YES! MATE
;
RETV LDX #$04 ; RESTORE
STX STATE ; STATE=4
;
; THE VALUE OF THE MOVE (IN ACCU)
; IS COMPARED TO THE BEST MOVE AND
; REPLACES IT IF IT IS BETTER
;
PUSH CMP BESTV ; IS THIS BEST
BCC RETP ; MOVE SO FAR?
BEQ RETP
STA BESTV ; YES!
LDA PIECE ; SAVE IT
STA BESTP
LDA SQUARE
STA BESTM ; FLASH DISPLAY
RETP LDA #"." ; print ... instead of flashing disp
Jmp syschout ; print . and return
;
; MAIN PROGRAM TO PLAY CHESS
; PLAY FROM OPENING OR THINK
;
GO LDX OMOVE ; OPENING?
BMI NOOPEN ; -NO *ADD CHANGE FROM BPL
LDA DIS3 ; -YES WAS
CMP OPNING,X ; OPPONENT'S
BNE END ; MOVE OK?
DEX
LDA OPNING,X ; GET NEXT
STA DIS1 ; CANNED
DEX ; OPENING MOVE
LDA OPNING,X
STA DIS3 ; DISPLAY IT
DEX
STX OMOVE ; MOVE IT
BNE MV2 ; (JMP)
;
END LDA #$FF ; *ADD - STOP CANNED MOVES
STA OMOVE ; FLAG OPENING
NOOPEN LDX #$0C ; FINISHED
STX STATE ; STATE=C
STX BESTV ; CLEAR BESTV
LDX #$14 ; GENERATE P
JSR GNMX ; MOVES
;
LDX #$04 ; STATE=4
STX STATE ; GENERATE AND
JSR GNMZ ; TEST AVAILABLE
;
; MOVES
;
LDX BESTV ; GET BEST MOVE
CPX #$0F ; IF NONE
BCC MATE ; OH OH!
;
MV2 LDX BESTP ; MOVE
LDA BOARD,X ; THE
STA BESTV ; BEST
STX PIECE ; MOVE
LDA BESTM
STA SQUARE ; AND DISPLAY
JSR MOVE ; IT
JMP CHESS
;
MATE LDA #$FF ; RESIGN
RTS ; OR STALEMATE
;
; SUBROUTINE TO ENTER THE
; PLAYER'S MOVE
;
DISMV LDX #$04 ; ROTATE
DROL ASL DIS3 ; KEY
ROL DIS2 ; INTO
DEX ; DISPLAY
BNE DROL ;
ORA DIS3
STA DIS3
STA SQUARE
RTS
;
; THE FOLLOWING SUBROUTINE ASSIGNS
; A VALUE TO THE MOVE UNDER
; CONSIDERATION AND RETURNS IT IN
; THE ACCUMULATOR
;
STRATGY CLC
LDA #$80
ADC WMOB ; PARAMETERS
ADC WMAXC ; WITH WHEIGHT
ADC WCC ; OF O25
ADC WCAP1
ADC WCAP2
SEC
SBC PMAXC
SBC PCC
SBC BCAP0
SBC BCAP1
SBC BCAP2
SBC PMOB
SBC BMOB
BCS POS ; UNDERFLOW
LDA #$00 ; PREVENTION
POS LSR
CLC ; **************
ADC #$40
ADC WMAXC ; PARAMETERS
ADC WCC ; WITH WEIGHT
SEC ; OF 05
SBC BMAXC
LSR ; **************
CLC
ADC #$90
ADC WCAP0 ; PARAMETERS
ADC WCAP0 ; WITH WEIGHT
ADC WCAP0 ; OF 10
ADC WCAP0
ADC WCAP1
SEC ; [UNDER OR OVER-
SBC BMAXC ; FLOW MAY OCCUR
SBC BMAXC ; FROM THIS
SBC BMCC ; SECTION]
SBC BMCC
SBC BCAP1
LDX SQUARE ; ***************
CPX #$33
BEQ POSN ; POSITION
CPX #$34 ; BONUS FOR
BEQ POSN ; MOVE TO
CPX #$22 ; CENTRE
BEQ POSN ; OR
CPX #$25 ; OUT OF
BEQ POSN ; BACK RANK
LDX PIECE
BEQ NOPOSN
LDY BOARD,X
CPY #$10
BPL NOPOSN
POSN CLC
ADC #$02
NOPOSN JMP CKMATE ; CONTINUE
;-----------------------------------------------------------------
; The following routines were added to allow text-based board
; display over a standard RS-232 port.
;
POUT jsr pout9 ; print CRLF
jsr pout13 ; print copyright
JSR POUT10 ; print column labels
LDY #$00 ; init board location
JSR POUT5 ; print board horz edge
POUT1 lDA #"|" ; print vert edge
JSR syschout ; PRINT ONE ASCII CHR - SPACE
LDX #$1F
POUT2 TYA ; scan the pieces for a location
match
CMP BOARD,X ; match found?
BEQ POUT4 ; yes; print the piece's color and
type
DEX ; no
BPL POUT2 ; if not the last piece, try again
tya ; empty square
and #$01 ; odd or even column?
sta temp ; save it
tya ; is the row odd or even
lsr ; shift column right 4 spaces
lsr ;
lsr ;
lsr ;
and #$01 ; strip LSB
clc ;
adc temp ; combine row & col to determine
square color
and #$01 ; is board square white or blk?
bne pout25 ; white, print space
lda #"*" ; black, print *
.byte $2c ; used to skip over LDA #$20
POUT25 LDA #$20 ; ASCII space
JSR syschout ; PRINT ONE ASCII CHR - SPACE
JSR syschout ; PRINT ONE ASCII CHR - SPACE
POUT3 INY ;
TYA ; get row number
AND #$08 ; have we completed the row?
BEQ POUT1 ; no, do next column
LDA #"|" ; yes, put the right edge on
JSR syschout ; PRINT ONE ASCII CHR - |
jsr pout12 ; print row number
JSR POUT9 ; print CRLF
JSR POUT5 ; print bottom edge of board
CLC ;
TYA ;
ADC #$08 ; point y to beginning of next row
TAY ;
CPY #$80 ; was that the last row?
BEQ POUT8 ; yes, print the LED values
BNE POUT1 ; no, do new row
POUT4 LDA REV ; print piece's color & type
BEQ POUT41 ;
LDA cpl+16,X ;
BNE POUT42 ;
POUT41 LDA cpl,x ;
POUT42 JSR syschout ;
lda cph,x ;
jsr syschout ;
BNE POUT3 ; branch always
POUT5 TXA ; print "-----...----- |
Last page update: October 21, 2002.