4Mhz Circuit with a 20Mhz PIC

[koossa]

Good day Picers!

I have layout an easy LED blink circtuit at 4Mhz.
I only have 20Mhz PICs, 1 x PIC16F877-20l/P and 2 x PIC16F877-20/P

When I program the PIC16F877-20l/P @ 4Mhz it works fine, but when I program the PIC16F877-20/P it does not work and it's exactly the same circuit.

Is there any setting to get this Pics working @ 4Mhz?


Thank you!
Koossa

[Kamikaze47]

I assume you have the following line at the top of your PBP program:

DEFINE OSC 4

Thats the only setting I can think of that you would need to worry about.

What does happen? Does everything happen at the wrong speed, or does the PIC refuse to do anything at all?

[koossa]

Here is my code, and nothing at all happen
With the PIC16F877-20l/P it is working, but when I switch it with the PIC16F877-20/P it does not work.


<code>
&nbsp;&nbsp;Include "Modedefs.bas"

&nbsp;&nbsp;DEFINE OSC 4 ' Set the Xtal frequency to 4mHz

&nbsp;&nbsp;LEDPin VaR PORTC.2
&nbsp;&nbsp;i var byte

Main:
&nbsp;&nbsp;for i = 1 to 10
&nbsp;&nbsp;&nbsp;&nbsp;High LEDPin
&nbsp;&nbsp;&nbsp;&nbsp;Pause 400
&nbsp;&nbsp;&nbsp;&nbsp;Low LEDPin
&nbsp;&nbsp;&nbsp;&nbsp;Pause 400
&nbsp;&nbsp;next i
end
</code>

[Jumper]

Hi,

At 20 MHz I guess you use "HS" for 20 MHz but for 4 MHz "XT" would be a better choice.

What do you clock it with? do you have a 4MHz x-tal or osc?

/me

[koossa]

Jumper

Thank you very much for your feedback.
I do have my Oscillator setting on "XT" and I'm using a 4Mhz X-tal.

Koossa

[paul borgmeier]

... a long shot but try blinking RB0 instead of RC2 (and report back).