Holtek HT-IDE, User Manual

Page: 198 / 258

Traffic Light
This application uses red, green and yellow LEDs to simulate a crossroads
traffic light function. Initially R1 and G2 are illuminated. After a delay the
green light flashes followed by the yellow light. After another delay R2 and
G1 are illuminated. This cycle will continue in this way indefinitely in the
same way as the traffic lights at a traffic crossroad intersection. Within the
application the different time durations for the red and green light as well
as the flashing time can be programmed.
Circuit design
The circuit uses the two port sections PA0~PA2 and PA4~PA6 with each one
representing a set of traffic lights on each road at a crossroad intersection.
The operation of the circuit will be self explanatory from the contents of the
program. See the circuit diagram for more details of the hardware.
Program
#include ht48c10.inc
;------------------------------------------------------------
data .section ’data’ ;== data section ==
count1 db ? ;delay loop counter 1
count2 db ? ;delay loop counter 2
count3 db ? ;delay loop counter 3
flash db ? ;light flash register
rglight db ? ;light register
;------------------------------------------------------------
code .section at 0 ’code’ ;== program section ==
org 00H ;
jmp start ;
org 04h ;external interrupt subroutine
reti ;for safeguard
HT-IDE User’s Guide
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