baud rate between USB->serial converter and AVR328 on UNO question [solved]

Projects Programming
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I am hoping to receive serial data over USB at at least 115200 on an UNOr3. I am using the Serial library.

I threw a scope probe on the AVR328 pin 2 and it looks as if the AVR8U2 is sending data out of its UART (to the AVR328P2) at 56kbps.

Question: is there a way to increase the baud rate between the USB to serial converter (AVR8U2) and the main AVR on the UNO?

56k seems terribly slow but it may be a limitation that is intentionally in place to allow the AVR328 more time between calls to empty its UART. My UNO isn't doing much other than receiving a packet and shoving it out the SPI port so I could like run at 250Kbps or higher without issue.

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I believe that sets the baud rate for the AVR328's UART, not what the USB->serial converter is transmitting at. On my oscilloscope the baud is the same regardless of how I init the serial library. In fact I get junk and a load of framing errors unless it is set to 56K.

4

Squando:
I believe that sets the baud rate for the AVR328's UART, not what the USB->serial converter is transmitting at. On my oscilloscope the baud is the same regardless of how I init the serial library. In fact I get junk and a load of framing errors unless it is set to 56K.

So even if you set the Arduino to 115200 and you set Serial Monitor to 115200 you can only use 56000 (not even 57600?).

5

As far as I've seen I only ever have 57.6k (you're correct, not 56k) between the AVR8U2 and the AVR328 (scoping AVR328 Pin 2 - RXD). Initializing the serial library with different baud rates does not have an effect.

You mentioned setting the baud rate on the serial monitor which is a good idea. I imagine there is some interface form the PC side that can set the baud rate on the TTL UART side of the AVR8U2. That would make perfect sense. I bet there is some command interface via the USB driver to set exactly what I am after. I likely have to set the baud rate from my PC based application.

6

Alright! That was it. I wasn't setting up the baud rate properly in my PC based host application and that seems to set the baud on the other side of the AVR8U2. Makes perfect sense now. :wink:

Thank you so much Johnwasser! Thanks to you I'm back to getting something accomplished this evening!