Craig:
I suspect that if you are aiming for an alphanumeric type keyboard that the PS2 style interface may be a distinct advantage to you. You described the requirement for your portable "access" device as being passive such that the microcontroller in the actual product being accessed would directly interface the keypad and LCD modules. If this is the case it seems not so convenient to run many many lines out the connector to support a raw matrix type keyboard. Thus you would end up having to implement some type of micrcontroller in the access device to scan the keyboard. On the other hand a ready made notebook computer replacement assembly such as that from Crystal with PS/2 interface requires a 2 wire serial connection plus power and ground.

If you were to also deploy a graphics type LCD panel, these are often also available with SPI type interface (clock and data serial) that I could anticipate a very low cost interfacing between the acess device and the products internal microcontroller. This scheme gives direct control of the access device to the main microcontroller software without having to undergo a separate microcontroller design to embed in the access device.

Michael Karas

PS...Plus prototyping can use any old keyboard you have laying around and the interface app notes to adapt such keyboard are easily found on the web. MJK