HP-97S I/O testing

[Hiwi]

Hi all,
i have a HP97S on my desk for repair. A friend acquired the calc recently on ebay.
Typical text from the seller: No magnetic card on hand so i could not test the reader, printer transport with minor problem and easy to fix with links to this forum, haha.

I never had a 97S, so i was exited to test the I/O function first. I fixed the battery. There were no test programs on magnetic cards nor the original testplug provided.

So I made a test interface with an Arduino micro. I took 4 data lines and multiplexed them to
4 x 8 Bit latches 74HCT373, CLK triggered from 4 other lines.

It took some time to figure out to activate the interface and adopt the logic (positve/negative)

Amazing how flexible this box is.

The interface can be triggered to accept data by one line, can send a kind of ACK and set 3(4) lines with simple SF/CF function to switch e.g. relay or leds.

The flag 3 enables the input from the interface directly to the display / keyboard buffer.
Sending a byte 'C' calls subroutine at label 'A'. So you have a simple program control.

The data input uses a simple serial line via usb.

A very nice machine. :-)