Pulse Train Generation
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.
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 = 0.1ms
b. TH = 0.1ms, TL = 0.3ms
Write an assembly program that generates a pulse train at the RA2 bit of PORTA for each of the following cases.
a. b. c.
TH = TL = 0.2ms
TH = 0.3ms, TL = 0.2ms
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.
- Do not use the Prescaler option.
- Do not modify any line of code of the LoopTime subroutine in the P0_template.asm file.
- Do not call the LoopTime subroutine more than once.
- 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 βdelayβ 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 Bβ11101111β, TRISB
where MOVLF is a macro defined as follows:
MOVLF macro literal, dest movlw literal
movwf dest endm