Objective: The experiment is designed to exhibit some of the capabilities of generating pulses at the ports of the PIC18F4520.
Specific Tasks:
Use the P0_template.asm file as a starting point in order to complete the following tasks.
1. Write an assembly program that generates a pulse train at the RA2 bit of PORTA for each of the following cases. a. TH = TL = 0.1ms
b. TH = 0.1ms, TL = 0.3ms
2. Write an assembly program that generates a pulse train at the RA2 bit of PORTA for each of the following cases. a. TH = TL = 0.2ms
b. TH = 0.3ms, TL = 0.2ms
c. TH = 0.25ms, TL = 0.35ms
By the end of this assignment you should have written five (5) different .asm files.
Notes:
Please observe the following items while working through this assignment.
1. Do not use the Prescaler option.
2. Do not modify any line of code of the LoopTime subroutine in the P0_template.asm file.
3. Do not call the LoopTime subroutine more than once.
4. Do not create a second subroutine similar to LoopTime.
Guidelines:
There are four distinct phases for the pulse train generation:
1. Configure the pins of the PORT as outputs.
2. Send your pulse to the configured pins using appropriate commands (review the following commands: btg, bsf, bcf).
3. Use conditional logic and a “delay” mechanism to control the duty cycle of the pulse trains.
4. Loop around indefinitely to generate a continuous pulse train.
To read or write anything from a port, it is necessary to configure the port pins accordingly, using the Special Function Register (SFR) TRISx, where x is the name of the port (e.g. TRISB configures the pins of port B).
In order to configure a pin as an output, put a 0 in the corresponding bit of TRISx. Similarly, to configure a pin as an input, put a 1 in the corresponding bit.
Example: to configure pin 4 of port B as an output and the others as inputs:
MOVLF B’11101111’, TRISB
where MOVLF is a macro defined as follows:
MOVLF macro literal, dest movlw literal
movwf dest endm
