I/O commutation time or bug ?

[firefox78]

I try to drive 2 ingectors at the same time with a PIC16F628 but with the follow code I have a big problem

output_low(PIN_A0);
output_low(PIN_A1);
delay_ms(15);
output_high(PIN_A0);
output_high(PIN_A1);
delay_ms(15);

Only the last I/O line (PIN_A1) works! I tryed to drive one line per time and all is ok so the lines work. The result will be a square wave on each line.

If I use the follow code

output_low(PIN_A0);
delay_ms(1);
output_low(PIN_A1);
delay_ms(15);

output_high(PIN_A0);
delay_ms(1);
output_high(PIN_A1);
delay_ms(15);

All work fine but 1ms between lines is too long for my application. What is the problem? Is a bug or each line takes some time for commutation?

Best regards.

[PCM programmer]

This is probably caused by the classic Read-Modify-Write problem.

The solution is to maintain a "shadow" register (a byte variable) in RAM
for all of your Port A pins. When you want to change the value of a
pin, you should change it in the Shadow register. Then write the
entire shadow register value to Port A in one operation. Don't do
individual bit set and clear operations.

See my large post in this thread. It has sample code which shows
how to implement a shadow register for Port A.
http://www.ccsinfo.com/forum/viewtopic.php?t=21825&start=15

Also, I'm assuming that you did everything else correctly on the 16F628,
such as disabling the comparators.

[firefox78]

Tank you very much. I will try your solution next week.

Best regards

[fuzzy]

I had simlar problem with PIC16F876.
Port A is analog in this MCU so I had to specify, (NO_ANALOG) in ADC setup to have a digital Port. I don't know wether in your pic PORT a is analog .