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

[CuriousOne]

Hello.

I'm building an push-pull converter driver using these chips. The code is as follows:

'PUSH PULL DRIVER

ANSELA = %00000000  'TURN OFF ANALOG  
TRISA=%00000000     'SET PORTS TO OUTPUT
OSCCON = %11111111  'SET INTOSC TO 32MHZ


tavuka:

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

GOTO TAVUKA

The problem is, that measured port OFF times are longer than ON times, as you can see on attached scope:



Any ideas how to fix this?

[richard]

OSCCON = %11111111 'SET INTOSC TO 32MHZ

looks wrong
OSCCON = %11110000 'SET INTOSC TO 32MHZ would be more appropriate assuming int osc and pll

porta.x = y on a 12f1840@32mhz is just asking for trouble use lata.x=y

[CuriousOne]

Yes, config is wrong, but problem is same at ANY clock speed.

Tried with LATA - no difference. ON time is about 220ns, OFF time is about 760ns. In terms of PWM, this means 50% duty, so another 50% is simply wasted.

[CuriousOne]

As I see, this is caused by loop, which returns program to beginning.

For example, I've tried to lengthen code by repeating commands 4 times without using loop, and 4 pulses are correct.

[pedja089]

I hope that you are kidding with us...
Here is your code explained:
tavuka:
PORTA.2=1'<turn on PORTA.2, need 4 osc clock to do that, then next instruction
PORTA.2=0'<turn off PORTA.2 need 4 osc clock to do that, then next instruction
PORTA.4=1'<4 clock to do this, but it doesn't do anything with PORTA.2
PORTA.4=0'<4 clock to do this, but it doesn't do anything with PORTA.2
GOTO TAVUKA '<4 or 8 clocks(can remember) to do this, but it doesn't do anything with PORTA.2
So when you count all clock, you have 4 osc clock long high state on PORTA,2, and 16 clock low state on PORTA.2.
Similar situation is with PORTA.4...
Program execute exactly what you are tell, Not what you want...

[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.

[Acetronics2]

the 1840 in ECCP half bridge mode looks to be fine too, no ???

Alain