Holtek HT-IDE, User Manual

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xor a,20h ; timer overflow register “XOR”
; with 20h
sz acc ; check over 20h
jmp timer_nov ; if not over 20h , jump timer_nov
mov a,00001011b ;
reti ;(4) ; return from ISR
timer_nov: ; timer_nov
clr acc ;
reti ; return ISR
start: ; program start
mov a,07h ;(1) ; setup INTC (external INT ON,
; timer ON)
mov intc,a ;
mov a,80h ; setup timer mode (internal clock)
mov mrc,a ;
clr pcc ; set port C as output port
top: ;(13) ; top
set pac ;(12) ; set port A as input port
set pbc ; set port B as input port
clr addrl ; clear low byte address register
clr addrh ; clear high byte address register
mov a,00001001b ; move acc=00001001,
; (BUSY=1, ACK=0, OE=0, WR=1)
mov pc,a ;(3) ; output acc to port C
clr acc ;
store: ; store
snz acc.0 ;(4) ; check acc.0=“0”.if external INT
; interrupt,will change acc.0=“1”
jmp store ; if acc.0=“0” jump store
clr pac ;(5) ; if acc.0=“1” , set port A as
; output port
clr pbc ; set port B as output port
next: ; next
mov a,addrl ;(6) ;
mov pa,a ; output low byte address register
; to port A
mov a,addrh ;
mov pb,a ; output low byte address register
; to port B
inc addrl ; increment low byte address register
sz addrl ; check if equal to 0
jmp no_inc ; if not 0 jump no_inc
mov a,1 ;
addm a,addrh ; increment high byte address
; register
no_inc: ; no_inc
mov a,00000010b ; move acc=00000010,
; (BUSY=0, ACK=0, OE=1,WR=0)
mov pc,a ;(7) ; output acc to port C
HT-IDE User’s Guide
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