Serial write garbled on Terminal program but OK on in-built Serial viewer

micro:bit micro:bit extensions
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My Serial writes are garbled when sent out to TeraTerm terminal program but Ok when viewed on the Serial monitor. Characters get dropped. This is quite useless as I want my class to receive the data in Python on the PC. I get this in both micro:bit Python editor and MS Makecode. I have used different micro:bits on different PCs, same result. I might just go back to installing micropython and download the script with ampy.

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Is TeraTerm doing serial over USB or are you using external pins for serial? Have you confirmed that you have the correct baud (115200)?

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Serial via USB, about 10% of characters dropped or changed so I doubt any Serial port settings. I use ESPXXX and Pi Pico like this all the time.

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I just tried MU Editor 1.2 and data is coming through with no errors.

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Oh, that’s interesting. I wonder if it’s just a flaw in TeraTerm (not enough buffer space or not polling fast enough?).

I don’t know that this would really help…but I have a JavaScript library (https://github.com/bsiever/microbit-webusb) that has an example webpage you could also try: https://bsiever.github.io/microbit-webusb/ .

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I use TeraTerm in the same mode with ESP and Pi Pico with no such issues. I also wrote python to read the serial and got the same dropped characters. It’s interesting how the Mu Editor produces code that works fine. I thought that Makecode might be running background event handling loops that were interfering with serial. Are you getting good comms with the microbit and Makecode?

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The JavaScript library had been dropping characters when it wasn’t polling the serial port fast enough, but currently I don’t have any significant problems with either MakeCode or the JavaScript library.

Can you share an example of the code you’re using to send data (an example that demonstrates the dropped/garbled data)? And what version of micro:bits are you using?

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Finally the solution:

Thanks for contacting the Micro:bit Educational Foundation.

When a WebUSB connection is used to send a program directly to micro:bit, MakeCode and the Python Editor stay connected and ready for incoming serial data.

With a serial terminal program connected, for some reason an occasional character still finds it’s way to WebUSB.

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Use the three dots menu on the Download/send to micro:bit button to Disconnect, or close the WebUSB connected browser tab.

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I have found this easy to forget. It’s taken a while, but I finally now do think “shut MakeCode” when serial is misbehaving!

For the same reason, having more than one tab with MakeCode or the Python Editor open can lead to errors.

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