12F683, 12LF1840 - Port ON/OFF speeds are different!

[CuriousOne]

Even if code is like this:

HEAD:
PORTA.2=1
PORTA.2=0
GOTO HEAD

the "goto" occupies much more time. Is there a way to shorten it?

[HenrikOlsson]

No, there's not way to shorten the execution time (in instruction cycles that is) of a GOTO. What you can do is to "lengthen" the time of the other instructions.

Head:
PortA.2 = 1
@ NOP   ' Two nops to compensate for the GOTO
@ NOP
PortA.2 = 0
GOTO Head

Obviously this will also change the frequency.

/Henrik.

[Gusse]

How about if you toggle pin in loop?

HEAD:
TOGGLE PORTA.2
GOTO HEAD

[CuriousOne]

I don't want to "lengthen" time, because it significantly lowers the frequency, from about 1mhz to 200khz, which is bad. I've found a partial workaround - I've inserted

PORTA.2=1
PORTA.2=0
PORTA.4=1
PORTA.4=0

16 times, so now having about 90% duty cycle, which is ok.

But, is there a way to fix this otherwise?

Try 18 series PIC, or 24 series?

[Heckler]

Have you considered doing this in assembly??

[pedja089]

It's same thing in ASM.
ASM
tavukaASM:
BSF PORTA,2
BCF PORTAM2
BSF PORTA,4
BCF PORTA,4
GOTO tavukaASM
ENDASM

That is ASM code equivalent of his PBP code.
Still same situation....

[Gusse]

Would it be easier to do this with PWM module? With 32MHz you can reach 4MHz output frequency and accurate duty cycle.
I think these PIC's have just one PWM module. If that is not enough, then select other which have more PWM outputs.
At least, trials can be run with your current PIC's.