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vcsdesigns
0 Posts |
 Posted - 06 Oct 2006 : 20:58:26
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I am aware that the PXA255 uses a 14.7456 Mhz clock and divides it down to get the baud rate/bps.
However, this division is rarely perfect.
Can you tell me the actual rate of the 115,200 baud setting on the BitsyXB board?
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akidder
1519 Posts |
Posted - 07 Oct 2006 : 08:30:59
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The BitsyXb uses a 13.000 MHz clock on the PXA270 (see section 6.3.10 of the user manual), resulting in a 115.044 kbps bit rate. That's an 0.14% error, which translates to an 1.4% over the usual ten bits (8,N,1). Most UARTS sample each bit 16 times, which allows for up to 6% error before even one of the samples fails.
Here are a few other baud rates and their bit rate error using a 13 MHz clock:
9.6k: 9.6012 (+0.01%)
19.2k: 19.202 (+0.01%)
38.4k: 38.348 (-0.1%)
115.2k: 115.044 (-0.1%)
On ADS PXA255 products (BitsyX, VGX, GCX and others), we use a 3.6864 MHz core clock, which divides evenly down to the common serial baud rates (9600, 19.2k, 38.4k, 115.2 kbps). |
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