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).

[koossa]

I have moved my LED to RB0 and change my code, but not one of them are working now.
Am I missing something?


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

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

&nbsp;&nbsp;LEDPin VaR PORTB.0
&nbsp;&nbsp;i var byte
Main:
&nbsp;for i = 1 to 10
&nbsp;&nbsp;High LEDPin
&nbsp;&nbsp;Pause 400
&nbsp;&nbsp;Low LEDPin
&nbsp;&nbsp;Pause 400
&nbsp;next i
end
</code>

[mackrackit]

Have you tried Oscillator setting on "HS"?

[koossa]

No
I will try

[koossa]

I have set it to HS, but still nothing.

[Bruce]

Attach the compiled .HEX file that you are programming into the PIC here. If there's a
problem with your config settings, that makes it easy for someone to spot.

[koossa]

Bruce

Attached the zipped hex file.

Thank you very much for your time!

[Bruce]

Hi Koossa,

The good news is - config settings look fine. XT osc, WDT on, PWRT on, brownout on,
LVP off, protection off. Looking good here if you're using a 4MHz external crystal.

The bad news is - this code isn't anywhere near what you show above just trying to
toggle an LED.

It sets up the USART for 19,200bps at 4MHz, shoots out a single letter f, then sits & spins
waiting for serial data input, in a loop watching the RCIF flag bit.

Are you 100% sure you're actually programming the file you expect into your 877?

The .HEX file you have attached is for sure not the one you show above trying to toggle
an LED....;o}

[Archangel]

Hello Koossa,
try adding this to your code:

CCP1CON = 0 ' DISABLE CAPTURE COMPARE MODULE
TRISC = %00000000 ' SET ALL PORT C TO OUTPUTS


JS

[Charles_Leo]

I think this code was compiled using the MicroCode Studio Plus ICD Compile. It won't run in the PIC unless there is an ICD connection to the PC.

If you intended to run the code without the ICD, find the "normal" compile/program buttons in MicroCode Studio Plus. Don't use ICD Compile or ICD Compile And Program unless you have the ICD connection hooked up.

[koossa]

I think this code was compiled using the MicroCode Studio Plus ICD Compile

Thank you Charles_Leo, you are correct, it's been a while since I last use this software so I was a bit rusty.

Joe S., I have added your code and everything is working now

CCP1CON = 0 ' DISABLE CAPTURE COMPARE MODULE
TRISC = %00000000 ' SET ALL PORT C TO OUTPUTS

Thank you very much!!!