Uno R4 Wifi Serial Baud Rates

Official Hardware UNO Family UNO R4 WiFi
1

I'm running into an issue setting the baud rate low on the Uno R4 Wifi. I can get it down to 4800, but anything lower that that looks like it freezes the board. I can reflash to set the baud rate higher again and recover and everything works as expected. and I have run the same code on other boards down at 2400bps with no issue.

I haven't seen anyone reporting this issue yet nor anything in the documentation that suggests it can't go that low on this board.

Thanks in advance!

2

Not at all familiar with the Uno R4 WiFi so can't help.

Is that the serial baud rate for communication with the PC (Serial)?
Or for communication over another Serial (e.g. Serial1)?

3

This is when I'm setting Serial (not Serial1)
But I can try tomorrow to see if i can set Serial in the range that works (4800 or higher) and then set Serial1 down at 2400 to see if there is a similar issue.

4

I'm doing some tests at the moment.

I can confirm that Serial1 functions down to 300 baud.
Like chamahawk, I can't get Serial to work below 4800 baud.

Here is an oscilloscope trace of 'Serial1' at 300Bd and 'Serial' on the serial monitor at 4800Bd:

Serial 4800Bd - Serial1 300Bd
Serial 4800Bd - Serial1 300Bd1360×592 293 KB

5

Wondering if the issue with Serial is with the main processor or with the ESP32 it connects to?

6

I had a quick look at the schematic. If the Renesas is the processor that provides the USB (I know there is some kind of switch between the two processors), baud rate is irrelevant (to my knowledge) as it's native USB.

But as said, not familiar at all

7

KurtE,
I noticed that when Serial is set to 2400 baud, the TX LED flashes.

I believe that this indicates that the RA41M is sending data to the ESP32, but the ESP32 isn't sending it out of the USB connector.

8

I am also rusty on this as I have not done much with these boards for a while.
But if my memory is correct:

By default:

If you are setup for USB Serial communications, the ESP32 is the processor talking to the host, more or less as a USB to Serial adapter. And it itself could care less about the Baud rate, except that it takes the setting that the host gave it, and it
sets it's UARTs baud rate to this, which needs to match the baud rate contained in the sketch, as the Renesas processor will use it to setup it's UART that talks to the ESP32 to that baud rate.

Caveat: If you are setup for USB type of HID, then the code sets the IO port which then sets up the Renesas processor to handle the USB communications.

Earlier I hacked up a R4 Wifi with a switch across the pads, and I set up a variant that
used it the same way the MINIMA does. I preferred running that way for a couple of reasons...

9

again it has been a while, but I believe that there are two pins on the ESP32 header that
have the signals coming to and from the RA4m1 processor. They will be the ESP32s 3.3v signal levels.

image
image599×223 35.1 KB

10

:+1: Life can be complicated.

11

Something to note is that 2400 and 1200 baud have a special significance to the UNO R4 WiFi:

https://arduino.github.io/arduino-cli/latest/platform-specification/#1200-bps-bootloader-reset

So it is expected that when you open a serial connection to the board at those specific baud rates, it will cause the board go into a special mode instead of operating normally.

However, that is specific to the 1200 and 2400 baud rates. It does not explain unexpected behavior you might have encountered at any other baud rates.

I know that problems have been reported about the use of 300 baud on other chips:

1 Like
12

Huge thanks to everyone for jumping on this. Really glad to see that it's not something on my side. I can definitely work around this knowing the limits.