Trouble starting PIC or internal clock on 12f683?

[PickyBiker]

I am using the program from Walter Dunckel (http://www.scalerobotics.com/stamps/...ssthrough.html). It is unchanged from what's on the web. The PIC doesn't start or the internal clock isn't running. I read the application note on troubleshooting power-up problems, but it still fails. Here is the situation and what I have tried.

Chip is 12f682, tried two of them.
Power is 5.19 VDC
2200uf cap across +5 and GND where it enters the breadboard (tried it without that too)
1uf cap across pins 1 & 8
Power up is via switch so the rise time of +5 is fast and without much ring.
Checked the wiring a half dozen times.
Originally, the input across the 3 diodes was falling at a long slope so I added a pull-down resistor. Now the receiver pulses look like what Walter shows on his o'scope.
Tried it with and without a pull-up resistor on pin 4, mclr
With the given _INTRC_OSC_NOCLKOUT , it never starts, but if I change it to _INTOSCIO I can get it to start very very occasionally.

By "not starting" I mean there are no output pulses to the servos. All output pins are just low.

Any thoughts on what else I can check?

[mackrackit]

Try changing

@ __config _INTRC_OSC_NOCLKOUT  & _WDT_OFF & _MCLRE_ON & _CP_OFF

to

@ __config _INTRC_OSC_NOCLKOUT  & _WDT_OFF & _MCLRE_OFF & _CP_OFF

[ScaleRobotics]

Oops.

Thanks Dave, and mgauthier711! I will correct that.

Walter

[PickyBiker]

Try changing

@ __config _INTRC_OSC_NOCLKOUT  & _WDT_OFF & _MCLRE_ON & _CP_OFF

to

@ __config _INTRC_OSC_NOCLKOUT  & _WDT_OFF & _MCLRE_OFF & _CP_OFF

The only way I can get it to start is with this:

@ __config _INTOSCIO & _WDT_ON & _MCLRE_OFF & _CP_OFF

Now that it starts, there is still an issue with it. I get output pulses on servos 2-4, but not on servo1. The pulses that I do get do not vary with the input pulses, they are just 2ms on 3 & 4, and 1.6 ms on 2.

I'll check to see if there is anything wrong with my setup and wiring again.

[ScaleRobotics]

The code does act funny if the input from the pulses exceeds the 1ms to 2ms range. Check your transmitter, and see if you have any channels above 100%. You might try changing them to 95% in both directions, just to make sure.

Walter

Edit:
Do you have the diodes on the three incomming receiver signals?

[PickyBiker]

Yes, the diodes are there and I get good 5v pulses just like on your web page. Current status:

all channels 85% with 0 offset and 0 subtrim.

No changes detected in output pulses.

Could the missing servo 1 pulse be because I have the WDT on? (Remember, it won't start if I set WDT off).

[ScaleRobotics]

Sorry to hear that.

Let me double check what I have when I get home tonight. I will let you know what I have, and double check my wiring to see if I differ from my schematic.

Thanks for the feedback.

Walter

[mackrackit]

The only way I can get it to start is with this:

@ __config _INTOSCIO & _WDT_ON & _MCLRE_OFF & _CP_OFF

Now that it starts, there is still an issue with it. I get output pulses on servos 2-4, but not on servo1. The pulses that I do get do not vary with the input pulses, they are just 2ms on 3 & 4, and 1.6 ms on 2.

I'll check to see if there is anything wrong with my setup and wiring again.

I have not had a chance to look at the data sheet but you OSC setting is bothersome.
That outputs a clock signal I think???

[Archangel]

Hello mgauthier711,
Just saw your post, did you try this with PWRTE on and WDT off? Sometimes these PICs are a little fussy about the power rise curve and the power up timer helps.

[PickyBiker]

Pulling pin 4 to +5v and removing the pull-down resistor from the input allows it to start reliably now with
@ __config _INTRC_OSC_NOCLKOUT & _WDT_OFF & _MCLRE_ON & _CP_OFF

It still only puts out fixed length pulses. If I put the pull-down back in 47k, the output stops. If I add as little as 20pf to the input, the pulses stop. There is improvement however, I now get fixed length pulses on all 4 outputs.
[ATTACH][/ATTACH]
If the attachment made it, you can see my wirng and the pulses