Some assembly language programmers may want to convert 6502 communications
software to use the IIGS logic boards to the full. To insure future
compatibility when using the Apple IIGS serial ports through assembly
language, you should use the built-in firmware calls. The firmware works very
well, is very fast, and also provides you with a built-in interupt handler
and input/output buffers. All of these features can be managed through ROM
calls.
More advanced use (bit and register handling) would require familiarity with
the "Z8030/Z8530 Serial Communication Chip Technical Manual" from Zilog.
Information there reveals that communications on the 8530 is much more
complicated than that on the 6551; a straight conversion may not be that
simple.
Zilog Inc.
210 Hacienda ave.
Campbell CA. 95008
Here are some examples of how you might use the serial ports with the
built-in firmware. NOTE: all these examples use the Pascal interface in the
ROM.
To initialize your programs and the port you might use something like this:
InitVector equ $C20D ; pointer to the init routine in ROM
ReadVector equ $C20E ; Pointer to the read char routine
WriteVector equ $C20F ; pointer to the Write routine
StatVector equ $C210
ExtendVect equ $C212 ; Pointer to the extended interface routine
InitPort equ $F8 ; set up some area's for indirect jumps
ReadChar equ $FA ; to be used in the program to make the
WriteChar equ $FC ; calls to ROM
StatusCall equ $FE ;
ExtendCall equ $F6 ; New vector for extended interface
InitPort lda InitVector ; First set up your indirect pointers
sta InitPort
ldy #$C2 ; make sure to set the high byte
sty InitPort+1
lda ReadVector
sta ReadChar
sty ReadChar+1
lda WriteVector
sta WriteChar
sty WriteChar+1
lda StatVector
sta StatCall
sty StatCall+1
lda ExtendVect
sta ExtendCall
sty ExtendCall+1
ldx #$C2 ; Now make the init call to the ROM
ldy #$20 ; Always set up the X and Y Regs first
jsr (InitPort) ; and indirect jump to the init routine
cpx #0 ; test for an error
beq *+5 ; if its zero skip next jump
jmp Error ; if non-zero an error occured call error rtn
RTS