Specifications

mikroElektronika | Free Online Book | PIC Microcontrollers | Appendix B: Examples
;************************************************************************
org 0x0000 ; Address of the first program instruction
banksel OSCCON ; Selects memory bank containing
; register OSCCON
bcf OSCCON,6 ; Selects internal oscillator LFINTOSC with
bcf OSCCON,5 ; the frequency of 31KHz
bcf OSCCON,4
bsf OSCCON,0 ; Microcontroller uses internal oscillator
banksel TRISB ; Selects bank containing register TRISB
clrf TRISB ; All port B pins are configured as outputs
banksel PORTB ; Selects bank containing register PORTB
loop
movlw B'01010101' ; Binary number 01010101 is written to W
movwf PORTB ; Number is moved to PORTB
movlw h'FF' ; Number hFF is moved to W
movwf counter1 ; Number is moved to variable "counter1"
loop1
decfsz counter1 ; Variable "counter1" is decremented by 1
goto loop1 ; If result is 0, continue. If not,
; remain in loop1
movlw B'10101010' ; Binary number 10101010 is moved to W
movwf PORTB ; Number is moved to PORTB
movlw h'FF' ; Number hFF is moved to W
movwf counter1 ; Number is moved to variable "counter1"
loop2
decfsz counter1 ; Variable "counter1" is decremented by 1
goto loop2 ; If result is 0, continue. If not,
; remain in loop2
goto loop ; Go to label loop
end ; End of program
EXAMPLE 3
Using nested loop
The connection scheme is again the same. To make this a bit more interesting, a different combination of port B bits
change each other. And, that’s not all of course. As seen from the previous two examples, the microcontroller is very fast
and often, it needs to be slowed down. The use of the built-in oscillator LF, as in example 2, is the last measure that
should be applied. The problem is more often solved by using nested loops in a program. In this example, the variable
"counter1" is decremented 255 times by 1 in the shorter loop1. Prior to leaving this loop, the program will countdown 255
times from 255 to 0. It means that between only two LED diode’s blink on the port, there are 255x255 pulses coming from
the quartz oscillator. Precisely speaking, the number of pulses amounts to approximately 196 000 since it also takes some
time to execute jump instructions and decrement instructions. Yes, it’s true, the microcontroller mostly waits and does
nothing...
Example 3:
;******************* Header ***********************************************
;************* DEFINING VARIABLES *****************************************
cblock 0x20 ; Block of variables starts at address 20h
counter1 ; Variable "counter1" at address 20h
counter2 ; Variable "counter2" at address 21h
endc
;**************************************************************************
org 0x0000 ; Address of the first program instruction
banksel TRISB ; Selects bank containing register TRISB
clrf TRISB ; Clears TRISB
banksel PORTB ; Selects bank containing register PORTB
loop
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