PIC16F57 timer how to trigger an interrupt

Question

I'm trying to make a simple delay turn-on function using Timer0 inside the PIC16F57 itself.All the example I can find on internet mostly come with build-in interrupt function which the PIC16F57 doesn't have,at least on the datasheet.Any way or hint to workaround?

Objective is quite simple:

1. a switch was pressed(input stay HIGH)
2. LED will turn ON after 3s
3. LED will remain ON if switch is still being pressed/latched
4. if switch input is LOW logic level,then LED will off

Did try with normal __delay_ms(3000) but it's not practical since switch off the LED also need to wait for 3s if the switch on routine is not completed.

I'm using MPLAB XIDE in C language and no way to change the mcu to other model as the PCB is already fixed for PIC16F57.

Answer 1

The PIC16F57 has no interrupts so everything must be done by polling. The trick with polling is to do it in a way that doesn't block other operations.

Instead of waiting for 3 seconds after detecting the switch closure, wait for a much shorter time eg. 30ms, increment a counter, then check the switch again. If the switch is now open then reset the counter and go back to waiting for the switch to close. If the counter reaches 100 the switch has been closed for 100*30ms = 3 seconds, so you can turn on the LED and then just wait for the switch to open.

This method is a simple form of cooperative multitasking, where each 'task' (checking the switch, counting time, operating the LED) gets control of the CPU in sequence. It relies on each task only 'running' for a short time before handing control to the next one, and storing its current state (in this case the time count) in static variables so it can pick up from where it was the last time it 'ran'. With careful coding you can make the MCU appear to be doing several things simultaneously.