SAME70 UART maximum baudrate? Maybe a bug in START?

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AndreaCan
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Posted by AndreaCan: Thu. May 17, 2018 - 08:33 AM
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I would like to understand from those who have experience in SAME70, what is the maximum possible baudrate with the UARTs, as there are some inconsistencies between the documentation and the START settings.

If I read the datasheet of SAME70 (DS60001527B) I see that in paragraph 59.13.1.10 there is written: In Asynchronous modes, the maximum baud rate that can be achieved is MCK2/8, if the bit USART_MR.OVER = 1. Example: if peripheral clock = 150 MHz, the maximum achievable baud rate is 18.75 MBit/s.

Also in the datasheet in paragraph 46.6.1.1 in the formula we can calculate that if OVER = 1 and CD = 1 with Clock = 150 MHz, the baudrate is really 18.75 MBit/s.

Instead in START if I create a new project with ATSAME70Q21B, I add the UART device (or USART used as UART), if I try to set the baudrate to 18.75 MBit / s appears the writing that says: Max value is 3000000.

So who is right? Is the datasheet wrong or does START have a bug?

 

Regards

Andrea

Best regards
Andrea

Tags:

Atmel SMART ARM-based MCUs and MPUs, Atmel Cortex-M MCUs, Atmel Start, UART, #SAME70 #SAM #SAME70Q21
Last Edited: Thu. May 17, 2018 - 08:35 AM
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jcandle
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Posted by jcandle: Thu. May 17, 2018 - 11:34 AM
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I have not tried it yet, but my assumption is:

You can set the registers to get 18.75MHz, but that does not guarantee the physical layer will have a sufficiently low bit error rate.  If the source and destination clocks are well matched and the transmission media (wiring) is good, it should work.  On the other hand, 3MB sounds like an arbitrary 'safe' limit.  IE, more of a "nanny-state" limit than a bug.

 

You can edit the settings in the start project and try it.

jeff

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AndreaCan
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Posted by AndreaCan: Thu. May 17, 2018 - 12:25 PM (Reply to #2)
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The "nanny-state" is fine but the START settings should be possible up to the maximum allowed in the specifications (as do other manufacturers for example STM), then it is up to the user to verify that the communication is done without problems (low bit error rate).

You can edit the settings in the start project and try it.

I can not edit the START setting, as it tells me that error. Maybe you mean that I can manually edit the source files and headers generated by start?

Yes, I could do it too. But currently I have not available the MCU for testing. If you have available the hardware part and you can do this test I would be very happy.

 

Thanks

Andrea

Best regards
Andrea

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jcandle
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Posted by jcandle: Thu. May 17, 2018 - 02:53 PM
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I have a SAME70 Xplained around here somewhere.  It won't be right away though... just a bit buried.

I kind of need to do this test between a PIC32MZ and a SAMD51 anyway...

jeff

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