Holtek HT-IDE, User Manual

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count1 db ? ;delay loop counter
mask db ? ;mask register
matrix db ? ;key matrix register
;------------------------------------------------------------
code .section at 0 ’code’ ;== program section ==
org 00h ;
jmp start ;
org 04h ;external interrupt subroutine
reti ;for safeguard
org 08h ;timer/event 0 interrupt subroutine
reti ;for safeguard
org 0ch ;timer/event 1 interrupt subroutine
reti ;for safeguard
start: ;
clr intc ;initialize registers
clr tmrc ;to guarantee performance
clr tmr ;(interrupts)
set pac ;(ports)
set pbc ;(input mode)
set pcc ;
main:
set pac ;(1) ;set port A to input mode
clr pbc ;set port B to output mode
clr pa ;zero port A (latch=0)
set pb ;off LEDs
keyloop: ;
mov a,0feh ;(2) ;scan first row of keys
mov matrix,a ;hold scan code
mov pac,a ;pa.0 output 0 (latch)
mov a,pa ;read input state
cpl acc ;;complement input state
and a,0f0h ;;
sz acc ;if any input?
jmp get_key ;yes. get input info
mov a,0fdh ;(2);no. scan second row
mov matrix,a ;hold scan code
mov pac,a ;pa.1 output 0 (latch)
mov a,pa ;read input state
cpl acc ;;complementl input state
and a,0f0h ;;
sz acc ;if any input?
jmp get_key ;yes. get input info
mov a,0fbh ;(2) ;no. scan third row
mov matrix,a ;hold scan code
mov pac,a ;pa.2 output 0 (latch)
mov a,pa ;read input state
cpl acc ;;complement input state
and a,0f0h ;;
sz acc ;if any input?
Chapter 15 Input/Output Applications
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