Interesting HP-65 card reader failure mode

[teenix]

Can the faulty 65 write a program to a card and read it back. That is the only option I have for testing, I don't have pre-recorded cards to test with.

With this limitation, I still cannot replicate the STO 4 error, but I'll keep trying.

It is hard to make sense of it, because the only way data can be entered into the buffer is via the HP-65 card command [memory insert] when a key is pressed in WPGM mode, otherwise this code is not executed.

STO 4 is program code [01]. This can't just be added to the buffer, it has to be inserted at the 1st program point and shift the buffer pointers as well. I am having trouble finding anywhere in code that might do this after the buffer is reset. I'll have to enable some traps to see if code is executing without permission.


Just a useless info tidbit...

The HP-65 uses 96 instructions to enter key [1] as a program step, the HP-67 uses 787 :-)

cheers

Tony