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[Solved] Internal serial (RPi port) vs Raspberry voltage mismatch  

Krzysztof Kaczor
New Member
Internal serial (RPi port) vs Raspberry voltage mismatch
Hi everyone. I'm making some experiments on Prusa's MK3S RAMBo board's internal serial port (the one, where Raspberry PI Zero is connected to) - J19. And something is completely not right to me, maybe you'll shed some light.
Based on the diagrams, J19 RXD pin is connected via voltage divider to Atmega UART1 RX port - fine, safe, great. But TXD port from J19 is wired DIRECTLY to Atmega UART1 TX port! RPi serial ports uses 3.3V logic, Atmega provides 5V logic on ALL serial ports. So based on this, RPi should blow up. And it works. What have I missed?
Moreover, when I connect serial converter working on 3.3 logic, I am able to send commands to prusa (i.e. M117 - to display text on LCD), but I am not able to receive anything... and it seems I've blown my serial converted because of the above.
Any thoughts?
Posted : 10/12/2020 11:51 pm
Krzysztof Kaczor
New Member
Topic starter answered:
RE: Internal serial (RPi port) vs Raspberry voltage mismatch

sorry my bad. voltage divider is on Tx port, not Rx! Case closed.

Posted : 11/12/2020 12:24 am