While working on a project I tried sending data from my Arduino NANO to ATMega64 placed on AREXX Robot arm PCB via TXD/RXD. After plugging in VCC, GND, TXD and RXD to UART socket it didn't work so I figured the socket itself must be backwords or mirror image from my perspective. Then I tried plugging everything in on the other side of the socket and as I plugged VCC to one of the pins a little smoke came out (I can't specify exact place where smoke came from) and from now on there is no connection to the robot. However LEDs seem to work just like before the 'incident'. It can be seen as COM but, desktop app constantly displays 'Connection failed' when trying to access the robot. It seems that I plugged VCC to the MRESET pin and GND to the RXD1 pin of the ATMega64. Can anyone help define if my processor is burnt? And if so, what can I do to fix the robot? Are there any other ways to send data to ATMega considering it is already programmed adn I want to keep it that way? Unfotunately, replacing ATMega isn't possible for me. Thanks in advance for any help.
Robot PCB :