Holtek HT-IDE, User Manual

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call delay ;(3) ;delay for a while
set c ;;shift lamp state left through
rlc lamp ;(4) ;;carry flag (fill LSB 1)
sz c ;if all LEDs have been lit?
jmp llamp ;(5) ;;no. continue shift left loop
rrc lamp ;(6) ;;yes. restore lamp state
rlamp: ;shift lamp right loop
mov a,lamp ;load lamp state
mov pa,a ;output lamp state to port A
call delay ;delay for a while
set c ;;shift lamp state right through
rrc lamp ;(7) ;;carry flag (fill MSB 1)
sz c ;if all LEDs have been lit?
jmp rlamp ;;no. continue shift right loop
rlc lamp ;;yes. restore lamp state
jmp llamp ;(8) ;repeat from shift lamp left loop
delay proc ;delay subroutine
mov a,2fh ;; set counters
mov count1,a ;;
mov count2,a ;;
d1:
sdz count2 ;count down count2
jmp d1 ;
sdz count1 ;count down count1
jmp d1 ;
ret
delay endp
end
Program description
This short program allows an array of 8 LEDs to be illuminated in turn first
in a left moving direction and then in a contrary right moving direction. The
program begins by first setting up the ports as either output or input as
shown in section (1). Here, as all ports are to be set as outputs, the control
register for PA, known as PAC should only contain zeros. In section (2) bit
0 of Port A is set low which illuminates the first LED. Section (3) is a time
delay to allow the LED illumination to be visible. In section (4) the RLC or
rotate left instruction is used to move the illuminated LED one step to the
left using the lamp register and the accumulator. At section (5) the lamp
register is tested for all zeros. If this is the case, all the LEDs have been
illuminated and the program jumps to the next section illuminating the
LEDs in turn, one step to the right. This time the RRC or rotate right
command is used as shown in section (6). A process similar to the above is
repeated as shown in section (7). Finally the lamp register is checked for all
zeros, which is an indication that all the LEDs have been illuminated. If so
the program repeats the cycle jumping back to the beginning as shown in
section (8) and starting the pattern with the left moving LEDs.
Chapter 15 Input/Output Applications
187