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RS-232 Baud Rate + 32 MHz Frequency Issue

 
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johna



Joined: 26 Jun 2007
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RS-232 Baud Rate + 32 MHz Frequency Issue
PostPosted: Tue Jun 26, 2007 11:21 am     Reply with quote

I'm trying to run a PIC 18F2480 at 32 MHz (8MHz * 4x Multiplier) with a baud rate of 10400. When I try this, I receive only garbage. Is there a certain limitation in the baud rate values I can use when running the PIC at a high frequency?

When I run the PIC at 16 MHz (4MHz * 4X Multiplier), the 10400 baud rate works just fine.

Thanks for the help.
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Tue Jun 26, 2007 1:23 pm     Reply with quote

The data sheet says the internal oscillator isn't very accurate.
Also, the PLL has a lot of jitter.

Look in Tables 27-7 and 27-8.
Internal oscillator accuracy is +/- 2% at 25 deg. C.
It's +/- 5% over a wider temperature range.
The PLL has +/- 2% jitter.

Do a test. Use the H4 fuse with an 8 MHz crystal (instead of the
internal oscillator). See if your problems go away.
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