Epson HX20 Interface

One of the nice things about older hardware is that a lot of it comes with expansion connectors or other ports that allow you to attach arbitrary hardware to it. The HX-20 is no exception and comes with an expansion port which allows access to the bus signals of the main processor (yes it has two - almost dual core). I wanted a simple IO port so breadboarded a simple 8 bit output latch and 8 bit input circuit using old fashioned 74 series logic.

As a more permanent solution I routed a PCB.

I then used an old PC HDD cable to attach to the HX20 which helpfully uses a standard 0.1" pitch IDC connector. Unhelpfully they have used a different numbering scheme to the rest of the world which means the pin numbers are all jumbled, but that's not and unsolvable problem, just an irritation.

The output port can be used to drive other hardware, I'm going to use this one to drive a relay module:

The bottom two bits of the data bus are wired up on this PCB, so you write to address &H5000 and D0 and D1 will end up latched in the output port. To read inputs you read the same memory location, again D0 and D1 are the data bits that are wired up.