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

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)
  1. USB connectivity

Or are USART and USB connectivity mutyally exclusive???

Regards,

JaaC

Reply to
jaac
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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)
  1. USB connectivity

Or are USART and USB connectivity mutyally exclusive???

Regards,

JaaC

Reply to
jaac

My reading of the data sheet 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

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Reply to
MK

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