Re: AT91SAM7S256-128-64-321 USB and USART usage (clocking)


"jaac" <jaime.aranguren@xxxxxxxxx> wrote in message
news:1144357700.726570.299560@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Hi,

I want to know if it is possible to use at the same time the USB and
UART peripheral on the AT91SAM7S256-128-64-321, with zero error on the
UART part.

The clocking scheme is what concerns me. As far as I understand you
have the main clock MCK from an external crystal (or clock signal). Is
MCK derived directly, I mean, does MCK have the same frequency as the
external crystal? The UART peripheral takes its input from either MCK
or MCK/DIV. USB needs a couple of clocks: clock from the PLL at 48MHz
and MCK.

So, what are the recommendded values of external clock and external PLL
filter if one needs:

1. Core running at 60 MHz
2. UART running at 115200 bps / 57600 bps / 38400 bps / 19200 bps /
9600 bps (possibility of using any of them)
3. USB connectivity

Or are USART and USB connectivity mutyally exclusive???

Regards,

JaaC


My reading of the data *** tells me that if you want to use USB the
maximum MCK you can use is 48MHz. This is because you must use PLL clock at
48, 96 or 192 MHz for USB but the MCK prescale only offers divide by 2, 4, 8
etc.
There is no problem with getting close to your UART frequencies with 48MHz
MCK.

Michael Kellett

www.mkesc.co.uk


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