Noise on PORTC.0 with PIC16F73

[passion1]

I forgot to say:
The noise on PORTC.0 is present during the off pulse

[passion1]

After reading another thread I added
LOW PORTC.0
just before the loop and this seemed to solve my problem!
Why would that be?
Isn't TRISC %11111000 supposed to set PORTC.0 as an output?

[Archangel]

After reading another thread I added
LOW PORTC.0
just before the loop and this seemed to solve my problem!
Why would that be?
Isn't TRISC %11111000 supposed to set PORTC.0 as an output?

Hello Passion1,
Yes TRISC <font color=red><b>=</b></font color>%11111000 will set RC0 as an output
LOW PORTC.0 is a RMW operation and the data sheet advises not to do this on portC of this chip. RC.0 shares TMR1clockin and osc functions so you want to disable those if using as a standard I/O so:
T1CON.0 = 0 'disable timer 1
CCP1CON=0 ' disable capture compare module which works with timer 1

Datasheet SEC. 4.3
"Since the TRIS bit override is in effect while peripheral is enabled, read-modify-write instructions (BSF, BCF, XORWF) with TRISC as destination should be avoided."

[passion1]

Joe

Thank you!
I used

T1CON.0 = 0 'disable timer 1
CCP1CON=0 ' disable capture compare module which works with timer 1

and that solved my problem completely!

[mister_e]

I have some doubt about it... @POR, Timer1 is already off, CCP as well.

What you experiment is indeed an RMW issue. You don't want to write to successive output bit by bit, this will cause some problem one day or another, and faster your OSC is, more chance you have to see it happen.

What you want to do is to write to the WHOLE PORT at once instead of single bits.

Here:
PORTC=7
PORTC=0
Goto Here

Use shadow register, modify it, then dump it to your specific PORT, that's my suggestion.

[Acetronics2]

Hi, Passion

What Kind of load do you have on portC.0 ???

Here, your signal might not be far from ... ~ 700 kHz ( at first sight ! 555 Khz ... at second sight )

Alain

[Archangel]

I have some doubt about it... @POR, Timer1 is already off, CCP as well.

What you experiment is indeed an RMW issue. You don't want to write to successive output bit by bit, this will cause some problem one day or another, and faster your OSC is, more chance you have to see it happen.

What you want to do is to write to the WHOLE PORT at once instead of single bits.

Here:
PORTC=7
PORTC=0
Goto Here

Use shadow register, modify it, then dump it to your specific PORT, that's my suggestion.

PortC value on POR,BOR xxxx xxxx
value on all other resets uuuu uuuu

PortC Data direction Register
value on all resets 1111 1111

My theroy is T1 osc was causing his noise.