MC6821 PIA CA1 Interrupt test program

caint.s

***
* PIA - CA1 Interrupt
*
* RyuStudio Nov. 2022
***
*
* Lambda-2022 PIA Adrs
p0da      equ $f008       ; PIA0 DA
p0ca      equ p0da+1      ; PIA0 CA
p0db      equ p0da+2      ; PIA0 DB
p0cb      equ p0da+3      ; PIA0 CB
p1da      equ $f010       ; PIA1 DA
p1ca      equ p1da+1      ; PIA1 CA
p1db      equ p1da+2      ; PIA1 DB
p1cb      equ p1da+3      ; PIA1 CB
*
* MikBug NIO Adrs
nio       equ $a606
* pdata1 entry
pdata1    equ $f17e
*
          org $8000
*
start     jsr initpia0    ; set all ports on PA and PB to inputs
          ldx #ca1handler
          stx nio
          ldaa #$01       ; configure CA1 interrupt; 
          staa p0ca
endl      bra endl
*
ca1handler tst p0ca        ; check bit7 of PIA0 CA
          bpl notca
          ldx #camesg
          jsr pdata1
          bra endhandl
notca     ldx #ncamesg
          jsr pdata1
endhandl  swi             ; force quit; clear stack data
*
camesg    fcb	$0d, $0a
        	fcc	'INTERRUPT VIA PIA0 CA'
	        fcb $0d, $0a, 4
ncamesg   fcb	$0d, $0a
        	fcc	'INTERRUPT SOURCE UNKNOWN'
	        fcb $0d, $0a, 4
*
initpia0  ldx #p0da
          jsr initport
          ldx #p0db
initport  clra
          staa 1,X        ; reset Cx, select DDRx
          staa 0,X        ; set DDRx ; all output
          ldaa #4         
          staa 1,X        ; select PRx
          rts
initpia1  ldx #p1da
          jsr initport
          ldx #p1db
          bra initport
*
          end

This is a test for MikBug NMI handler NIO.