Timing Lapse in PICs

[Vizier87]

Hi guys,

I've been programming my PICs quite successfully until the communications part (SPI, UART) completely bugged me down.

Then I experimented with the timing of the PIC (with a 20MHz osc) using an oscilloscope and found out something pretty interesting. I set a program to blink an LED at 1 ms interval, and surprisingly the Scope indicated a 2ms interval! When I changed my Oscillator settings in Edit Project to 10 MHz, only then it gives a correct output of 1 ms interval.

I wonder if this is common? Please advise, gurus.

Thanks.
Vizier87

 

[Nigel Goodwin]

Hi guys,

I've been programming my PICs quite successfully until the communications part (SPI, UART) completely bugged me down.

Then I experimented with the timing of the PIC (with a 20MHz osc) using an oscilloscope and found out something pretty interesting. I set a program to blink an LED at 1 ms interval, and surprisingly the Scope indicated a 2ms interval! When I changed my Oscillator settings in Edit Project to 10 MHz, only then it gives a correct output of 1 ms interval.

I wonder if this is common? Please advise, gurus.

Only 'common' in that you either programmed it or set it incorrectly.

If 10MHz runs twice as fast as 20MHz, then it wasn't running at 20MHz - only 5MHz.

 

[Vizier87]

so how should I set it? The settings are as shown below, please advise:
**broken link removed**

These settings work well for other peripherals, until I worked on the USART/Serial.

Thanks Nigel.

 

[Nigel Goodwin]

You have PLL enabled, and divide by 5 - turn those off.

 

[Vizier87]

Well the thing is, the options in the box are as follows (I've arranged them for the pertinent details):

**broken link removed**

I'm not sure how to turn off PLL here, or the divide... Can you please be a bit more specific?

Thanks.