; centronics.679 - centronics printer driver for C64, in 6502 Assembler
; author Neil Franklin, last modification unknown (estimated 1986)
;                       this disassembly/source reconstruction 2000.06.07

; extracted from C64 with:
; load "centronics.679",8,1
;  5 k = 679
; 10 for i = k to k+240 step 16
; 15 print i
; 20 for j = i to i+15
; 30 print peek (j)
; 40 next j
; 50 input a$
; 60 next i

; hardware needed: Cable C64 user/RS232 port to centronics printer
;   port B (pins CDEFHJKL) Data out, port A bit 2 (pin M) strobe
;   ICR Flag bit (pin B) printer ready for char

; decimal dump     | hex listing    | disassembly ; comments

                                      *= $02A7

; 02A7-02BF unused by Commodore, 02C0-02FF res for Sprite 11

679: 173   0 221   | 02A7: AD 00 DD | LDA $DD00
       9   4       |       09 04    | ORA #$04    ; port A "TxD" pin on
     141   0 221   |       8D 00 DD | STA $DD00
     169  16       |       A9 10    | LDA #$10
     141  13 221   |       8D 0D DD | STA $DD0D   ; ICR Flag pin reset
     173   2 221   |       AD 02 DD | LDA $DD02
695:   9   4       |       09 04    | ORA #$04    ; port A "TxD" pin output
     141   2 221   |       8D 02 DD | STA $DD02
     169 255       |       A9 FF    | LDA #$FF
     141   3 221   |       8D 03 DD | STA $DD03   ; port B all pins output
     169 207       |       A9 CF    | LDA #$CF
     141  38   3   |       8D 26 03 | STA $0326   ; Output Vector LO
     169
711:               |       A9 02    | LDA #$02
     141  39   3   |       8D 27 03 | STA $0327   ; Output Vector HI = 02CF
     169   0       |       A9 00    | LDA #$00
     240  18       |       F0 12    | BEQ $02E1   ; rest init output "0"

; come from ROM system call FFD2, there JMP ($0326), to F1CA

      72           | 02CF: 48       | PHA         ; save output date
     165 154       |       A5 9A    | LDA $9A
     201   4       |       C9 04    | CMP #$04    ; char to printer?
     240   3       |       F0 03    | BEQ $02D9
      76
727:     205 241   |       4C CD F1 | JMP $F1CD   ; not, use standard routine
                                                  ; without PHA and LDA $9A
     173  13 221   | 02D9: AD 0D DD | LDA $DD0D
      41  16       |       29 1F    | AND #$10
     240 249       |       F0 F9    | BEQ $02D9   ; wait for Flag pin
     104           |       68       | PLA         ; re-get output data
     141   1 221   | 02E1: 8D 01 DD | STA $DD01   ; write to port B
     173   0 221   |       AD 00 DD | LDA $DD00
743:  41 251       |       29 FB    | AND #$FB
     141   0 221   |       8D 00 DD | STA $DD00   ; "TxD" pin off
       9   4       |       09 04    | ORA #$04
     141   0 221   |       8D 00 DD | STA $DD00   ; "TxD pin back on = strobe
      24           |       18       | CLC         ; system call was successfull
      96           |       60       | RTS
                   | 02F3:          |