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Diffstat (limited to 'wozmon.s')
| -rw-r--r-- | wozmon.s | 160 |
1 files changed, 160 insertions, 0 deletions
diff --git a/wozmon.s b/wozmon.s new file mode 100644 index 0000000..b26561e --- /dev/null +++ b/wozmon.s @@ -0,0 +1,160 @@ +; The WOZ Monitor for the Apple 1 +; Written by Steve Wozniak in 1976 + + +; Page 0 Variables + +XAML = $24 ; Last "opened" location Low +XAMH = $25 ; Last "opened" location High +STL = $26 ; Store address Low +STH = $27 ; Store address High +L = $28 ; Hex value parsing Low +H = $29 ; Hex value parsing High +YSAV = $2A ; Used to see if hex value is given +MODE = $2B ; $00=XAM, $7F=STOR, $AE=BLOCK XAM + + +; Other Variables + +IN = $0200 ; Input buffer to $027F +KBD = $D010 ; PIA.A keyboard input +KBDCR = $D011 ; PIA.A keyboard control register +DSP = $D012 ; PIA.B display output register +DSPCR = $D013 ; PIA.B display control register + + .org $FF00 + .export RESET + +RESET: CLD ; Clear decimal arithmetic mode. + CLI + LDY #$7F ; Mask for DSP data direction register. + STY DSP ; Set it up. + LDA #$A7 ; KBD and DSP control register mask. + STA KBDCR ; Enable interrupts, set CA1, CB1, for + STA DSPCR ; positive edge sense/output mode. +NOTCR: CMP #'_'+$80 ; "_"? + BEQ BACKSPACE ; Yes. + CMP #$9B ; ESC? + BEQ ESCAPE ; Yes. + INY ; Advance text index. + BPL NEXTCHAR ; Auto ESC if > 127. +ESCAPE: LDA #'\'+$80 ; "\". + JSR ECHO ; Output it. +GETLINE: LDA #$8D ; CR. + JSR ECHO ; Output it. + LDY #$01 ; Initialize text index. +BACKSPACE: DEY ; Back up text index. + BMI GETLINE ; Beyond start of line, reinitialize. +NEXTCHAR: LDA KBDCR ; Key ready? + BPL NEXTCHAR ; Loop until ready. + LDA KBD ; Load character. B7 should be ‘1’. + STA IN,Y ; Add to text buffer. + JSR ECHO ; Display character. + CMP #$8D ; CR? + BNE NOTCR ; No. + LDY #$FF ; Reset text index. + LDA #$00 ; For XAM mode. + TAX ; 0->X. +SETSTOR: ASL ; Leaves $7B if setting STOR mode. +SETMODE: STA MODE ; $00=XAM, $7B=STOR, $AE=BLOCK XAM. +BLSKIP: INY ; Advance text index. +NEXTITEM: LDA IN,Y ; Get character. + CMP #$8D ; CR? + BEQ GETLINE ; Yes, done this line. + CMP #'.'+$80 ; "."? + BCC BLSKIP ; Skip delimiter. + BEQ SETMODE ; Set BLOCK XAM mode. + CMP #':'+$80 ; ":"? + BEQ SETSTOR ; Yes. Set STOR mode. + CMP #'R'+$80 ; "R"? + BEQ RUN ; Yes. Run user program. + STX L ; $00->L. + STX H ; and H. + STY YSAV ; Save Y for comparison. +NEXTHEX: LDA IN,Y ; Get character for hex test. + EOR #$B0 ; Map digits to $0-9. + CMP #$0A ; Digit? + BCC DIG ; Yes. + ADC #$88 ; Map letter "A"-"F" to $FA-FF. + CMP #$FA ; Hex letter? + BCC NOTHEX ; No, character not hex. +DIG: ASL + ASL ; Hex digit to MSD of A. + ASL + ASL + LDX #$04 ; Shift count. +HEXSHIFT: ASL ; Hex digit left, MSB to carry. + ROL L ; Rotate into LSD. + ROL H ; Rotate into MSD’s. + DEX ; Done 4 shifts? + BNE HEXSHIFT ; No, loop. + INY ; Advance text index. + BNE NEXTHEX ; Always taken. Check next character for hex. +NOTHEX: CPY YSAV ; Check if L, H empty (no hex digits). + BEQ ESCAPE ; Yes, generate ESC sequence. + BIT MODE ; Test MODE byte. + BVC NOTSTOR ; B6=0 STOR, 1 for XAM and BLOCK XAM + LDA L ; LSD’s of hex data. + STA (STL,X) ; Store at current ‘store index’. + INC STL ; Increment store index. + BNE NEXTITEM ; Get next item. (no carry). + INC STH ; Add carry to ‘store index’ high order. +TONEXTITEM: JMP NEXTITEM ; Get next command item. +RUN: JMP (XAML) ; Run at current XAM index. +NOTSTOR: BMI XAMNEXT ; B7=0 for XAM, 1 for BLOCK XAM. + LDX #$02 ; Byte count. +SETADR: LDA L-1,X ; Copy hex data to + STA STL-1,X ; ‘store index’. + STA XAML-1,X ; And to ‘XAM index’. + DEX ; Next of 2 bytes. + BNE SETADR ; Loop unless X=0. +NXTPRNT: BNE PRDATA ; NE means no address to print. + LDA #$8D ; CR. + JSR ECHO ; Output it. + LDA XAMH ; ‘Examine index’ high-order byte. + JSR PRBYTE ; Output it in hex format. + LDA XAML ; Low-order ‘examine index’ byte. + JSR PRBYTE ; Output it in hex format. + LDA #':'+$80 ; ":". + JSR ECHO ; Output it. +PRDATA: LDA #$A0 ; Blank. + JSR ECHO ; Output it. + LDA (XAML,X) ; Get data byte at ‘examine index’. + JSR PRBYTE ; Output it in hex format. +XAMNEXT: STX MODE ; 0->MODE (XAM mode). + LDA XAML + CMP L ; Compare ‘examine index’ to hex data. + LDA XAMH + SBC H + BCS TONEXTITEM ; Not less, so no more data to output. + INC XAML + BNE MOD8CHK ; Increment ‘examine index’. + INC XAMH +MOD8CHK: LDA XAML ; Check low-order ‘examine index’ byte + AND #$07 ; For MOD 8=0 + BPL NXTPRNT ; Always taken. +PRBYTE: PHA ; Save A for LSD. + LSR + LSR + LSR ; MSD to LSD position. + LSR + JSR PRHEX ; Output hex digit. + PLA ; Restore A. +PRHEX: AND #$0F ; Mask LSD for hex print. + ORA #'0'+$80 ; Add "0". + CMP #$BA ; Digit? + BCC ECHO ; Yes, output it. + ADC #$06 ; Add offset for letter. +ECHO: BIT DSP ; DA bit (B7) cleared yet? + BMI ECHO ; No, wait for display. + STA DSP ; Output character. Sets DA. + RTS ; Return. + + BRK ; unused + BRK ; unused + +; Interrupt Vectors + + .WORD $0F00 ; NMI + .WORD RESET ; RESET + .WORD $0000 ; BRK/IRQ |