The PS/2 pins are D2 for DATA and D3 for Clock
PS2 mouse also needs 5V and ground

The pins used can be changed if required.

// PS2 mouse pins
#define DATA_PIN 2
#define CLOCK_PIN 3


Assuming you choose I2C1 for the CMM2 end:
On my nano, the I2C pins are 
A4 SDA connect to pin 3 on the CMM2 and 
A5 SCL connect to pin 5 on the CMM2

For I2C2 on the CMM2 the pins are
A4 SDA connect to pin 27 on the CMM2 and 
A5 SCL connect to pin 28 on the CMM2

For the serial, I used a voltage divider to reduce the 5V on the nano to ~3.3V on the CMM2/micromite.
If you use COM1, connect the Tx pin via a divider to pin 10 on the CMM2.
For the voltage divider, I use 1.8k in series and 3.3k to ground or 1.2k/2.7k whichever I find first.

You don't need any connection to the CMM2 TX pin. We don't send anything to the Nano.
Serial is fixe3d at 19200 baud and is not required.



