The circuit this month is a simple 8 light chaser built around a PIC. This will demonstrate how easy it is to program a PIC and to utilize it in a circuit. The circuit works as follows. When power is supplied to the circuit the PIC resets and starts to process instructions that are programmed into it. The program will turn on each LED in sequence with a small delay between each one. It will continue to do this until power is removed. The nice feature with this circuit is that you can program it to perform many complex lighting sequences. Normally you would have to rebuild a hardware based circuit to change the light sequence. With a PIC all you need to do is reprogram it and plug it back into the circuit. I am assuming that you will be using an IC socket. The circuit is show below and then I will discuss the program that is programmed into the PIC.
Click here to download the full size of the above Circuit.
The program is listed below:
;Assembly code for PIC16F84 micro controller
;Blinks LED's on the outputs in a rotating pattern.
;With 75khz osc, each LED stays on half a second.
; (its a 16F84,RC Oscillator, watchdog timer off, power-up timer on)
_config _RC_OSC &_WDT_OFF &_PWRITE_ON
;Declare variables at 2 memory locations.
J equ H'1F' ;J=Address hex 1F
K equ H'1E' ;K=Address hex 1E
org 0 ;start at address 0
;Set port B as output and initialize it
movlw B'00000000' ;w : =00000000 binary
tris PORTB ;port B ctrl register := w
movlw B'00000001' ;w := 00000001 binary
movwf PORTB ;port B itself := w
;Rotate the bits of port B leftward
mloop: rlf PORTB,f
;Waste some time by executing nested loops.
movlw D'50' ;w := 50 decimal
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