This is not a question. I think it's a bug (or maybe because my china arduino MEGA and UNO) and should be described at I have been weeks to discovered it.

Firstly I have at MEGA Tx19 and Rx18. And UNO RX0 and TX1. !Upsidedown Matrixkey web¡

MatrixKey wiring page says I have to join MEGA Tx with UNO Rx but this is not ok for me.
It only works joining Tx19 with Tx1 and Rx18 with Rx.
May 22 in General Questions by

1 Answer

It's because you have those mega board that have wrong labels for Serial #1 (but correct functionality, as serial #0, #2 and #3 which all are correct labeled).

You should connect exactly as it's described on the page: pin#18 from master to the slave Rx and pin #19 to the slave Tx.


May 22 by
Thanks Vlad. I think the same.

Worst of all, I have two MEGAs from apparently different china producer, but pin 18 are both RX instead an original MEGA Tx.
It's absolutely not critical.
I also have one of this board (it used in my test platform), and it is totally fine.

It's nothing wrong with pin 18  - it is Tx1 as it should be of course, just lettering as Rx1.

And it's easy to figure out, looking on other serial ports.