;-----------------------------------------------------------------
; EX83.ASM  Using the TRAP Interrupt.
;
; C.P. Diduch, 2001
;
; This program uses the single step or trap interrupt to branch
; control to an interrupt handler that writes the return address
; to output port 0x0003.
;
;    Author(s):
; Signature(s):                              Date:
;-----------------------------------------------------------------
;	.ORG	0x0000		; "assign to RAM"
	.DS     1		; "interrupt vector 0"
	.DS	1		; "interrupt vector 1"

; MAIN PROGRAM			; void main(void) {
				;
	.ORG	0x8000		; "assign the following to ROM"
				;
	ADDL	R0, NULL, 1	; "initialize interrupt vector"
        ADDL    R1, NULL, SS    ;
	DSTOREM	(R0), R1	;
	ORL#	FL, FL, 0x0020	; "set TF"
				; do {
M0:     NOP                     ;
        NOP                     ; "each of these instructions
        NOP                     ;  is interrupted"
        NOP                     ;        
        NOP                     ;
	JMP	M0		;    }

;-----------------------------------------------------------------
; void interrupt SS(void)
;
; Single step or Trap interrupt handler, SS, displays the return 
; address at output port 0x0003 with each interrupt.
;
SS:                             ; void interrupt SS(void) {
	STOREP	0x0003, RAI	; outport(3, RAI) ;
        CALL    DELAY, RA       ; "wait long enough to see
        RETI                    ;  display"
				;
;-----------------------------------------------------------------
; void DELAY(void)
;
; Procedure DELAY() implements  a software delay via a 'nested'
; decrement of registers R0 and R1. The procedure modifies 
; registers R1, R0 and FL.
;
DELAY:				; void DELAY(void) {
        ADDL    R1, NULL, 0x800 ; 
D0:     ADDL    R0, NULL, 0x040 ;
D1:     SUBL    R0, R0, 1       ;
	JMPNZ	D1		;
        SUBL    R1, R1, 1       ;
	JMPNZ	D0		;
	DJMP	(RA)		;