Possible replacement for a CRC

[teenix]

(10-18-2022 11:19 PM)Kostas Kritsilas Wrote:  From what I know, the HP-41's card reader can read HP-67 cards (and it does some translation magic between the HP-67 programs and the HP-41's programs). It seems logical that the HP-41 should be able to verify the HP-67 card's CRC to ensure that there isn't a read error. The algorithms for calculating/verifying the CRC codes for both machines are present in the IC that does that. I think that most likely, because both sets of calculations are present (and only one is in the HP-67's equivalent IC), and the completely different CPUs of the HP-67 and HP-41, that the ICs themselves would not interchange. I remember reading that some of the mechanical parts are common (and somewhat improved on the HP-41 card reader), but the electronics (all of the electronics) are completely different.

I think Alberto was referring to the (Card Reader Controller) CRC IC, not how the checksum is calculated.

The checksum in the HP-67 and 97 is generated and tested in ROM code, not by the IC. I'm not sure about the 41, but I assume it would be the same. It is simply the addition of the data words being written to the card, and this total is also written to the card. As the words are being read back they are added again and finally subtracted from the recovered checksum and if the result = 0, then all is ok - well, should be ok :-)

cheers

Tony