!NEC MPi400: Reverse Engineering the Keyboard Matrix

Introduction#

To be able to use the handheld, it's important to have a fully working keyboard.
The most needed information for this is a complete matrix of keys.

The connection to the keyboard matrix is done with two FPCs. One carries the signals for the rows while the other one handles the columns.

Hardware#

I went on and ordered a breakout PCB to measure the keyboard matrix.
With this PCB I will be able to measure the connection matrix and make notes where which key sits (logically).

Unfortunately I ordered the PCB prior changing the name of the Handheld.
It was !NEC MP900, but I changed it to !NEC MPi400 to make clear it's based on a Pi4.

I'm now waiting for the PCB to arrive. When it's here, I will post another entry containing all measured informations.