nRF52840 USB CDC ACM baud rate question

RE: nRF52840 USB CDC ACM baud rate question

Nguyen Hoan Hoang — Fri, 17 Jan 2020 13:30:40 GMT

CDC can be set at any baudrate, it does not matter.

RE: nRF52840 USB CDC ACM baud rate question

juulee — Fri, 17 Jan 2020 10:37:35 GMT

I have a question to you!

I'm going to develop nRF52840 USB CDC, receiving data from BLE and send it to PC.

I'm planning to check data using terminals, for example tera term or putty.

Terminals require baud rate, but in case of USB example, it doesn't have "baud rate".

Do you know how to set baud rate in terminals? Is it ok to set whatever I want?

Thanks!

RE: nRF52840 USB CDC ACM baud rate question

Nguyen Hoan Hoang — Tue, 16 Apr 2019 17:20:27 GMT

I think you can use the UART flow control signal for that. You can set CTS/RTS bit and in the CDC should receive it. It's in the USB standard CDC control line state.

RE: nRF52840 USB CDC ACM baud rate question

Philip — Tue, 16 Apr 2019 16:01:00 GMT

Yes I think so. It seems to drop the odd 64 byte packet now and again, when running on a slower windows machine. I have some C# software implementing the serialport. It works well on most computers.

Going back to my original question, I was trying to find a way to slow down the CDC data throughput from the nRF52840, but don't think the baudrate setting can be changed.

RE: nRF52840 USB CDC ACM baud rate question

Nguyen Hoan Hoang — Tue, 16 Apr 2019 15:20:31 GMT

This might be related to the window software that you use to get the data. I assume you are using some kind of terminal program. I use CoolTerm. Works well on MAC/Linux/Windows.

RE: nRF52840 USB CDC ACM baud rate question

Philip — Mon, 15 Apr 2019 15:08:09 GMT

Thanks. Yes I am thinking the same thing, that it is as fast as USB will allow.

The issue is on the Windows USB side I think, it seems to drop a few bytes from the 64K message on slower windows 10 machine. Ok on our windows 7 machines. In fact it is loosing 64 bytes somewhere, which is a USB packet now I think about it.

RE: nRF52840 USB CDC ACM baud rate question

Nguyen Hoan Hoang — Mon, 15 Apr 2019 15:01:55 GMT

I have not work with nRF CDC but worked with other MCU. By my experience, the baud rate is only for the physical UART. The CDC is virtual and always at USB speed. You are having issue on the UART side or USB side ?