Analyze UART data using logic analyzer?

Hardware UNO R4 UNO R4 WiFi
1

I just got my Uno R4 WiFi the other day, and took my first steps with the plug and make kit. Next I found my old Bitscope and thought it would be fun looking into some communication protocols using the logic analyzer.

I thought looking into the UART serial communication would be good as a starter, but unlike on the Uno 3 the serial used by USB doesn't seem to be the same as the one at pins 0 and 1. Does the Uno 4 provide any other pins that I can hook up the probes to when looking at the communication over USB between the Uno and my PC?

Thanks!

2

Welcome to the forum

The Serial object on a Uno R4 does not use pins 0 and 1, rather it goes directly to the USB interface and the data is not available on any normally accessed pins

Pins 0 and 1 are used by the Serial1 interface

3

Thanks for the confirmation! I will run this little exercise on the Uno R3 instead.

4

Many modern MCUs use full speed native USB for serial communications, in which case the baud rate and other communications parameters are often ignored.

5

If you are willing to sacrifice a USB lead then it would, of course, be trivial to tap into it to peek at what is going on with the Serial interface

6

I believe there are test points on the board where you can get the data lines from the USB.

7

With the R4 WiFi it really depends on your USB Configuration.

If your R4 is configured for normal Serial output, it is NOT using the USB Serial, instead the USB is connected up to the ESP32 processor on board, and the main processor talks to the ESP32, through a UART. So in this case, the Baud rate is important, as while it is not
needed for the ESP32 to talk through the USB it is needed for the ESP32 to know what Baud rate it should use to talk to the UART on the RA4M1...

Actually two of the UARTS of the R4 are connected to the ESP32, through level shifter
through the level shifter, as shown on Schematic:

image
image946×243 68 KB

It has been a while since I played with it, so I don't remember if the pins on the ESP Header
also shown in the above schematic were the ones used for the Seril UART, or for the other UART that is used to communicate Wifi and BTE data between the ESP32 and the RA4M1.

But you might try probing the two pins on the HEADER the TXD0/RXD0 which would be
the 3.3v version of the communications.

However if your T4 is configured for HID communications, like keyboard/mouse, then a switch (IO Pin 408) is pulled high (Or you solder the jumper SJ1),
image

Then the USB of the RA4M1 is connected up to USB and the baud rate does not matter
(For the most part)...

2 Likes
8

Thanks all for the help! It was especially interesting to learn about how the main processor talks to the ESP32 when using the USB Serial. I didn't expect that, but it was a good learning!

I have now been able to look into some protocols using my Bitscope. I now also remember why I didn't use the Bitscope that much, as the PC application is a bit on the slow side - to say it nicely. Back in the day I thought it was due to the RPi that I had connected it to, but now I also see the same when connected to a decent PC, but that is another story.