HP97 The journey begins

[teenix]

Hi all,

Still testing the HP-67 CPU replacement and appears to be going ok.


I have made some progress on the HP-65 CPU board replacement.

The PCBs should be here next week, the code has been written and mostly tested, so I should have one assembled soon and if the circuit works, start debugging.

While sorting out the code that does the CRC emulation for the 65 card read/write I noticed something. The read/write data is reversed in the 65 which may explain the incompatibility issues mentioned in the 65/67 restoration threads.

The sense chip parts are listed as

1826-0158 for 65

1826-0322 for 67,97,82104A

The circuits for the 65 and 67 show the same pin outs on these chips.

However, on checking the data with an oscilloscope I see the data reversal.

HP-65
RA and WA are associated with read/write [1] bits
RB and WB are associated with read/write [0] bits

HP-67
RA and WA are associated with read/write [0] bits
RB and WB are associated with read/write [1] bits

So swapping the sense chip between calculator models should still work as long as you only use cards that were read/written with the same sense chip.

cheers

Tony