PROGRAM LISTING: 86-09/TRACER.M65
0100 ; BASIC TRACER
0110 ; BY KEVIN GEVATOSKY
0120 ; (c) 1986, ANTIC PUBLISHING
0130 STMCUR = $8A ;Line # of cur. BASIC statement
0140 SRCPNT = $CB
0150 DESPNT = $CD
0160 TIMVAL = $CF ;Delay timer
0170 ZPOINT = $D0
0180 ROMOFF = $FF ;BASIC ROM 'off'
0190 SDLSTL = $0230
0200 CH = $02FC
0210 SOURCE = $A000
0220 STGO = $A97E
0230 DESTIN = $5000
0240 SKCTL = $D20F
0250 PORTB = $D301 ;ROM switch
0260 STARTCODE = $0100
0270 *= $0100
0280 RAMBAS
0290 JSR SETUP
0300 JMP MOVE ;Move BASIC
0310 SETUP
0320 LDA # <SOURCE ;Set ZP-pointer to start
0330 STA SRCPNT ;address of move.
0340 LDA # >SOURCE
0350 STA SRCPNT+1
0360 LDA # <DESTIN ;Set another pointer to
0370 STA DESPNT ;end address.
0380 LDA # >DESTIN
0390 STA DESPNT+1
0400 LDX #32 ;32 blocks=8K of BASIC code.
0410 LDY #0
0420 RTS
0430 MOVE
0440 LDA (SRCPNT),Y ;Copy BASIC ROM to RAM
0450 STA (DESPNT),Y
0460 DEY
0470 BNE MOVE
0480 ;
0490 NXTPAGE
0500 INC SRCPNT+1
0510 INC DESPNT+1
0520 DEX ;Decrement to next block.
0530 BPL MOVE
0540 ;
0550 LDA #ROMOFF ;Turn off BASIC ROM.
0560 STA PORTB
0570 JSR SETUP ;Set up pointers for next move.
0580 MOVE2
0590 LDA (DESPNT),Y ;Move BASIC source code
0600 STA (SRCPNT),Y ;to RAM at $A000
0610 DEY
0620 BNE MOVE2
0630 ;
0640 NXTPG2
0650 INC SRCPNT+1
0660 INC DESPNT+1
0670 DEX
0680 BPL MOVE2
0690 ;
0700 SETVEC
0710 LDA # <VECTOR ;Put a vector in BASIC
0720 STA $A978 ;which points to our routine.
0730 LDA # >VECTOR
0740 STA $A979
0750 JMP START ;Go set up DL.
0760 *= $0600
0770 ;
0780 ; *** MODIFY DISPLAY LIST ***
0790 START
0800 JSR DLSET
0810 JMP SOURCE ;JuMP to init. RAM-BASIC.
0820 DLSET
0830 LDA SDLSTL ;Move start address of DL
0840 SEC ;back two bytes to make room for
0850 SBC #2 ;more DL data.
0860 STA SDLSTL
0870 STA CHECK ;Save low byte of addr.for later.
0880 STA ZPOINT ;Set up zero-page pointer
0890 BCS NODEC ;to point at new DL start addr.
0900 ;
0910 DEC SDLSTL+1
0920 NODEC
0930 LDA SDLSTL+1
0940 STA ZPOINT+1
0950 LDY #0
0960 NXTBYT
0970 LDA DLDATA,Y ;Get data to modify DL
0980 STA (ZPOINT),Y ;and store it at new add.
0990 INY
1000 CPY #5
1010 BNE NXTBYT ;Do until done.
1020 ;
1030 FIND
1040 LDA (ZPOINT),Y ;Find end of the DL
1050 CMP #65 ;(65=ANTIC JMP to start of DL.)
1060 BEQ FOUND ;Got it!
1070 ;
1080 INC ZPOINT
1090 BNE NOINC
1100 ;
1110 INC ZPOINT+1
1120 NOINC
1130 JMP FIND ;Keep looking until found.
1140 FOUND
1150 INY ;Point to byte after ANTIC JMP
1160 LDA SDLSTL ;Store start adr of new DL
1170 STA (ZPOINT),Y ;for the ANTIC JMP.
1180 INY
1190 LDA SDLSTL+1
1200 STA (ZPOINT),Y
1210 LDA DLDATA+3 ;Set zero pg. ptr. to start
1220 STA ZPOINT ;of screen RAM for new
1230 LDA DLDATA+4 ;GR.0 mode line
1240 STA ZPOINT+1
1250 LDA #$80 ;Inverse blank
1260 LDY #39
1270 INVERT
1280 STA (ZPOINT),Y ;Store inverse chars
1290 DEY
1300 BPL INVERT ;Do for all 40 bytes.
1310 ;
1320 RTS
1330 ; *** TRACE ROUTINE ***
1340 VECTOR
1350 PHA ;Save reg.A for BASIC.
1360 LDA CHECK ;Get low byte of DL and
1370 CMP SDLSTL ;check to see if still same.
1380 BEQ CONT ;It is, so go on
1390 ;
1400 JSR DLSET ;Set up DL again.
1410 CONT
1420 LDA #0
1430 LDX #5
1440 BLANK
1450 DEX ;Zero out DECVAL
1460 STA DECVAL,X
1470 BNE BLANK
1480 ;
1490 NEXT
1500 LDY #0
1510 LDA (STMCUR),Y ;Get low byte of BASIC
1520 STA LOBYTE ;and save it.
1530 INY
1540 LDA (STMCUR),Y ;Get hi byte
1550 STA HIBYTE
1560 LDY #0
1570 ;Convert binary to decimal.
1580 SUBTRACT
1590 LDA LOBYTE
1600 SEC
1610 SBC DECPLC,Y ;Subtract decimal value
1620 STA TEMPLO ;from binary value.
1630 LDA HIBYTE
1640 SBC DECPLC+1,Y
1650 STA TEMPHI
1660 BCS DECSTOW ;Branch if OK
1670 ;
1680 INY ;Increment to next dec. place
1690 INY
1700 INX ;and increment counter.
1710 CPX #5 ;All done?
1720 BEQ DECOUT ;Yes? Then put it on screen.
1730 ;
1740 BNE SUBTRACT ;No? Subtract next dec. place
1750 ;
1760 DECSTOW
1770 INC DECVAL,X
1780 LDA TEMPLO
1790 STA LOBYTE
1800 LDA TEMPHI
1810 STA HIBYTE
1820 JMP SUBTRACT
1830 DECOUT
1840 LDX #4
1850 LDY #22 ;Pos. on screen.
1860 NXTCH
1870 LDA DECVAL,X ;Get decimal value.
1880 ORA #$90 ;Convert to ATASCII
1890 STA (ZPOINT),Y ;& display it.
1900 DEY
1910 DEX
1920 BPL NXTCH ;Do until done.
1930 ;
1940 NODEL
1950 LDA SKCTL ;Check keypress.
1960 CMP #$FF
1970 BEQ RESTOR ;If no keypress
1980 ;
1990 LDA CH
2000 CMP #156 ;Check CTRL-ESC
2010 BEQ EXIT ;If pressed then skip delay.
2020 ;
2030 RESTOR
2040 LDA #$FF ;Restore CH
2050 STA CH
2060 LDY #0 ;Zero timer.
2070 STY 20
2080 DELAY
2090 LDA 20 ;Get timer value.
2100 LSR A ;Divide by 2 for better resolution
2110 CMP TIMVAL
2120 BNE DELAY ;Delay until time is up.
2130 ;
2140 EXIT
2150 PLA ;Give Acc. A back to BASIC
2160 JMP STGO
2170 DECVAL .DS 5
2180 TEMPLO .DS 1
2190 TEMPHI .DS 1
2200 LOBYTE .DS 1
2210 HIBYTE .DS 1
2220 CHECK .DS 1
2230 DLDATA .BYTE $70,$70,$42,$00,$04
2240 DECPLC .WORD 10000,1000,100,10,1
2250 *= $02E0
2260 .WORD STARTCODE
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