The PIC comparator is the least used peripheral but it is just as fast as
the standard LM311...
Note: This information is applicable to any PIC Microcontroller that has a built in comparator.
There is one comparator in the 12F675 which you can set up in many different
ways and you can even supply a comparison voltage from an internal reference.
This voltage can be set to any of 32 steps.
This is just a simple project designed to show simple operation so that you can
use it. It shows all you need to do to operate the comparator.
The comparator is high speed with a specification of between 150ns to 400ns (150ns typ , 400ns max).
The typical response time is better than the standard response time of an LM311
which is 200ns - but you may get up to 400ns for the PIC comparator - thats
still very good.
Note This is one of the strengths of the comparator module - the fact
that it operates independently from the processor and has an extremely fast
response time.
One piece of information that is only implied by the documentation is that the comparator inputs must be set to analogue inputs - otherwise the comparator does nothing!
So you need to control ANSEL.
Circuit.
Download.
Code.
Comparator Modes.
Registers associated with the
comparator.
CMCON Comparator control
register.
VRCON Comparator voltage reference
control.
The following table shows the eight different ways of configuring the
comparator:
These are the registers for controlling the Comparator and Voltage
reference:
The main controls are:
...the rest are for interrupt control and I/O Direction (don't forget ANSEL
not in table!)
Download code here : Click to
download.
The following code sets up the comparator as a fully external device i.e.
the internal voltage reference is not used:
///////////////////////////////////////////////////////
// // File: 16F675_comparator.c // // Author: J F Main. // // Description: // // Use comparator GP0,GP1,GP2 // // Compiler : mikroC, mikroElektronika C compiler // for Microchip PIC microcontrollers // Version: 6.2.0.0 // // Note Testing: // // Tested on 12F675 // // Requirements: // // Target : 12F675 // // Notes : // // Uses internal oscillator. // // Version: // 1.00 Initial release. // // Copyright : Copyright © John Main // https://www.best-microcontroller-projects.com // Free for non commercial use as long as this entire // copyright notices included in source code // and any other documentation. // /////////////////////////////////////////////////////// /////////////////////////////////////////////////////// // Definitions #define COMPARATOR_OP 2 #define LED 4 /////////////////////////////////////////////////////// void init_ports(void) { //GP0 & GP1 are inputs TRISIO = 0 | (1<<GP0) | (1<<GP1); // 0 - op, 1 - ip ANSEL = (1<<GP0) | (1<<GP1); ; // Ana. ip on GP0 GP1 } /////////////////////////////////////////////////////// void init_comparator(void) { // Comparator with external input and output. // Cout = 0 (comparator output), Cinv =0 (inversion) CMCON = 0x01; } /////////////////////////////////////////////////////// // Start here void main() { int i; init_ports(); // Show device is active on power up. for (i=0;i<5;i++) { GPIO |= (1<<COMPARATOR_OP); delay_ms(100); GPIO &= ~(1<<COMPARATOR_OP); delay_ms(100); } init_comparator(); while(1) {; GPIO |= (1<<LED); delay_ms(100); GPIO &= ~(1<<LED); delay_ms(100); } } |
Note: To run
the above code you may need to remove the ICSP connections after
programming as the comparator pins are on the PGD and PGC lines. The code simply flashes the comparator output LED 5 times at start up and after this the comparator is turned on. Then the second LED is flashed continuously. By changing the POT setting you can see the comparator output turn on and off. |
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