BY
S. WOZNIAK
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*******SWEET 16 INTERPRETER
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R0L EQU $0 R0H EQU $1 R14H EQU $1D R15L EQU $1E R15H EQU $1F SAVE EQU $FF4A RESTORE EQU $FF3F ORG $F689 AST 32 JSR SAVE ;PRESERVE 6502 REG CONTENTS PLA STA R15L ;INIT SWEET16 PC PLA ;FROM RETURN STA R15H ;ADDRESS SW16B JSR SW16C ;INTERPRET AND EXECUTE JMP SW16B ;ONE SWEET16 INSTR. SW16C INC R15L BNE SW16D ;INCR SWEET16 PC FOR FETCH INC R15H SW16D LDA #>SET ;COMMON HIGH BYTE FOR ALL ROUTINES PHA ;PUSH ON STACK FOR RTS LDY #$0 LDA (R15L),Y ;FETCH INSTR AND #$F ;MASK REG SPECIFICATION ASL ;DOUBLE FOR TWO BYTE REGISTERS TAX ;TO X REG FOR INDEXING LSR EOR (R15L),Y ;NOW HAVE OPCODE BEQ TOBR ;IF ZERO THEN NON-REG OP STX R14H ;INDICATE "PRIOR RESULT REG" LSR LSR ;OPCODE*2 TO LSB'S LSR TAY ;TO Y REG FOR INDEXING LDA OPTBL-2,Y ;LOW ORDER ADR BYTE PHA ;ONTO STACK RTS ;GOTO REG-OP ROUTINE TOBR INC R15L BNE TOBR2 ;INCR PC INC R15H TOBR2 LDA BRTBL,X ;LOW ORDER ADR BYTE PHA ;ONTO STACK FOR NON-REG OP LDA R14H ;"PRIOR RESULT REG" INDEX LSR ;PREPARE CARRY FOR BC, BNC. RTS ;GOTO NON-REG OP ROUTINE RTNZ PLA ;POP RETURN ADDRESS PLA JSR RESTORE ;RESTORE 6502 REG CONTENTS JMP (R15L) ;RETURN TO 6502 CODE VIA PC SETZ LDA (R15L),Y ;HIGH ORDER BYTE OF CONSTANT STA R0H,X DEY LDA (R15L),Y ;LOW ORDER BYTE OF CONSTANT STA R0L,X TYA ;Y REG CONTAINS 1 SEC ADC R15L ;ADD 2 TO PC STA R15L BCC SET2 INC R15H SET2 RTS OPTBL DFB SET-1 ;1X BRTBL DFB RTN-1 ;0 DFB LD-1 ;2X DFB BR-1 ;1 DFB ST-1 ;3X DFB BNC-1 ;2 DFB LDAT-1 ;4X DFB BC-1 ;3 DFB STAT-1 ;5X DFB BP-1 ;4 DFB LDDAT-1 ;6X DFB BM-1 ;5 DFB STDAT-1 ;7X DFB BZ-1 ;6 DFB POP-1 ;8X DFB BNZ-1 ;7 DFB STPAT-1 ;9X DFB BM1-1 ;8 DFB ADD-1 ;AX DFB BNM1-1 ;9 DFB SUB-1 ;BX DFB BK-1 ;A DFB POPD-1 ;CX DFB RS-1 ;B DFB CPR-1 ;DX DFB BS-1 ;C DFB INR-1 ;EX DFB NUL-1 ;D DFB DCR-1 ;FX DFB NUL-1 ;E DFB NUL-1 ;UNUSED DFB NUL-1 ;F * FOLLOWING CODE MUST BE * CONTAINED ON A SINGLE PAGE! SET BPL SETZ ;ALWAYS TAKEN LD LDA R0L,X BK EQU *-1 STA R0L LDA R0H,X ;MOVE RX TO R0 STA R0H RTS ST LDA R0L STA R0L,X ;MOVE R0 TO RX LDA R0H STA R0H,X RTS STAT LDA R0L STAT2 STA (R0L,X) ;STORE BYTE INDIRECT LDY #$0 STAT3 STY R14H ;INDICATE R0 IS RESULT NEG INR INC R0L,X BNE INR2 ;INCR RX INC R0H,X INR2 RTS LDAT LDA (R0L,X) ;LOAD INDIRECT (RX) STA R0L ;TO R0 LDY #$0 STY R0H ;ZERO HIGH ORDER R0 BYTE BEQ STAT3 ;ALWAYS TAKEN POP LDY #$0 ;HIGH ORDER BYTE = 0 BEQ POP2 ;ALWAYS TAKEN POPD JSR DCR ;DECR RX LDA (R0L,X) ;POP HIGH ORDER BYTE @RX TAY ;SAVE IN Y REG POP2 JSR DCR ;DECR RX LDA (R0L,X) ;LOW ORDER BYTE STA R0L ;TO R0 STY R0H POP3 LDY #$0 ;INDICATE R0 AS LAST RESULT REG STY R14H RTS LDDAT JSR LDAT ;LOW ORDER BYTE TO R0, INCR RX LDA (R0L,X) ;HIGH ORDER BYTE TO R0 STA R0H JMP INR ;INCR RX STDAT JSR STAT ;STORE INDIRECT LOW ORDER LDA R0H ;BYTE AND INCR RX. THEN STA (R0L,X) ;STORE HIGH ORDER BYTE. JMP INR ;INCR RX AND RETURN STPAT JSR DCR ;DECR RX LDA R0L STA (R0L,X) ;STORE R0 LOW BYTE @RX JMP POP3 ;INDICATE R0 AS LAST RESULT REG DCR LDA R0L,X BNE DCR2 ;DECR RX DEC R0H,X DCR2 DEC R0L,X RTS SUB LDY #$0 ;RESULT TO R0 CPR SEC ;NOTE Y REG = 13*2 FOR CPR LDA R0L SBC R0L,X STA R0L,Y ;R0-RX TO RY LDA R0H SBC R0H,X SUB2 STA R0H,Y TYA ;LAST RESULT REG*2 ADC #$0 ;CARRY TO LSB STA R14H RTS ADD LDA R0L ADC R0L,X STA R0L ;R0+RX TO R0 LDA R0H ADC R0H,X LDY #$0 ;R0 FOR RESULT BEQ SUB2 ;FINISH ADD BS LDA R15L ;NOTE X REG IS 12*2! JSR STAT2 ;PUSH LOW PC BYTE VIA R12 LDA R15H JSR STAT2 ;PUSH HIGH ORDER PC BYTE BR CLC BNC BCS BNC2 ;NO CARRY TEST BR1 LDA (R15L),Y ;DISPLACEMENT BYTE BPL BR2 DEY BR2 ADC R15L ;ADD TO PC STA R15L TYA ADC R15H STA R15H BNC2 RTS BC BCS BR RTS BP ASL ;DOUBLE RESULT-REG INDEX TAX ;TO X REG FOR INDEXING LDA R0H,X ;TEST FOR PLUS BPL BR1 ;BRANCH IF SO RTS BM ASL ;DOUBLE RESULT-REG INDEX TAX LDA R0H,X ;TEST FOR MINUS BMI BR1 RTS BZ ASL ;DOUBLE RESULT-REG INDEX TAX LDA R0L,X ;TEST FOR ZERO ORA R0H,X ;(BOTH BYTES) BEQ BR1 ;BRANCH IF SO RTS BNZ ASL ;DOUBLE RESULT-REG INDEX TAX LDA R0L,X ;TEST FOR NON-ZERO ORA R0H,X ;(BOTH BYTES) BNE BR1 ;BRANCH IF SO RTS BM1 ASL ;DOUBLE RESULT-REG INDEX TAX LDA R0L,X ;CHECK BOTH BYTES AND R0H,X ;FOR $FF (MINUS 1) EOR #$FF BEQ BR1 ;BRANCH IF SO RTS BNM1 ASL ;DOUBLE RESULT-REG INDEX TAX LDA R0L,X AND R0H,X ;CHECK BOTH BYTES FOR NO $FF EOR #$FF BNE BR1 ;BRANCH IF NOT MINUS 1 NUL RTS RS LDX #$18 ;12*2 FOR R12 AS STACK POINTER JSR DCR ;DECR STACK POINTER LDA (R0L,X) ;POP HIGH RETURN ADDRESS TO PC STA R15H JSR DCR ;SAME FOR LOW ORDER BYTE LDA (R0L,X) STA R15L RTS RTN JMP RTNZ
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