2nd Serial on Velleman K8400 board for MMU2 (1 reply)

Hello All,

To take my printer to the next level I want to install a MMU2.

I think I got the most of it cleared out for my self. But I have big challenge: The MMU board needs a serial connection from the Printer to handle the commands. I checked which one is available but all the pins suitable are being used... (see attached schema of the main board) According to my information these pins are available for serial communication:

RX0: 00 PE0 Used for host communication (USB )
TX0: 01 PE1 Used for host communication (USB )

RX1: 19 PD2 unused (and no place on the board to connect this one)
TX1: 18 PD3 used for Zstop

RX2: 17 PH0 used for rotary encoder (I dont have schema of the LCD print but I traced the leads and checked the firmware's actual number)
TX2: 16 PH1 used for roraty encoder

RX3: 14  PJ1 used for Ystop
TX3: 15  PJ0 unused (and no place on the board to connect this one)

at this moment I think I have 2 options
- investigate SoftwareSerial (but how?? I don't think it is a good idea to use input interrupts in marlin)
- Replace the mainboard (which I don't like because I also need to replace the LCD etc)

But is there another option? Does anyone have an idea?

On the schematic lower right corner you'll have the connection to the LCD/encoder/SDcard
The connections on the schematic PK4-PG1 are easy accessible, I already have pin header on it for the bed-leveling.

Thanks in advanced, Martijn