I'd like to do some kind of proof of concept to get
the 2600 to send 1 byte through a joystick port to the
PC reliably.
Anyone have a webpage that shows how to create a cable
for this?
I think I found a good code snippet to use from here:
http://xi6.com/files/7800dump.asm
I chopped out the register save/restore and
flag-clearing and the use of a temp byte of RAM. Let
me know if you see any problems with it or if it can
be compressed further.
; Configure joystick port for OUT232 once
RELCODE LDA #$40 ; configure bit 6 for output
STA SWACNT
;-----------------------------------------------------------------------;
; Output a character as RS-232 through the joystick
port
;
; note: 6.5 lines = approx one 2400 baud bit
; 13 lines = approx one 1200 baud bit
;-----------------------------------------------------------------------;
; These constants add up to two bit times
;BIT1 EQU 13 ; 1200 baud
;BIT2 EQU 13
BIT1 EQU 7 ; 2400 baud
BIT2 EQU 6
OUT232 LDX #0 ; output low for start bit
STX SWCHA
LDX #4 ; init count for 4 bit pairs
LDY #BIT1 ; wait 1 bit
JSR WSYNCY ; send the start bit
OUT232b ROR ; rotate out next bit
ROR
ROR
STA SWCHA
LDY #BIT2 ; wait 1 bit
JSR WSYNCY ; send the next bit
ROR ; rotate out next bit
ROR
ROR
STA SWCHA
LDY #BIT1 ; wait 1 bit
JSR WSYNCY ; output next bit
DEX ; decrement counter
BNE OUT232b ; loop until 8 bits sent
; STA WSYNC ; adjust timing a little bit
LDA #$FF ; output high for stop bit
STA SWCHA
LDY #BIT1 ; wait 1 bit
JSR WSYNCY ; send the stop bit
RTS
;-----------------------------------------------------------------------;
; wait for number of scan lines specified in Y
register
;-----------------------------------------------------------------------;
WSYNCY STY WSYNC ; wait a line
DEY ; decrement line counter
BNE WSYNCY ; loop until done
RTS
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