HP97 The journey begins

[teenix]

Hi all,

I decided to have a go at making a HP-55 CPU replacement board and as of today it seems to be running ok.

Image below.

The module will run with the HP-55 crystal in place, or if the crystal is broken you can tell the PIC to output 784KHz from one of its IO pins to provide a clock source to the anode driver once the HP crystal has been removed. The PIC is running from its own crystal so the frequency should be reasonably stable for the timer.

The clock signal appears on one of the unused pins on the keyboard and a small wire is required to be soldered from there to a solder pad for the now vacant crystal.

I have put some memory on the module to store up to 100 programs which can be transferred via Bluetooth to a PC.

I was playing with the 55 emulator and I can use one of the unused programming codes to load one of those programs into HP memory while a program is running. I'm not sure if this is useful as you cannot GTO outside the normal program memory space and each new program would start at step 1. Still you could have a program that is made up of 4900 steps.

The emulator can also use the key sequence [f][BST] to clear the program memory when in PRGM mode. I still have to add this to the CPU board.

These changes do not affect the original HP-55 Microcode.

I have also started to put together a small crystal controlled circuit for the HP-45 timer. It only has a few components, so may go for around $Aus10.00 if anyone is still interested in such things.

cheers

Tony