HP-67 - 1612A03018 - Card Reader Advice Requested (was HP-67 - strange behavior)

[AndiGer]

(11-02-2019 11:22 PM)teenix Wrote:  The speed control is determined by battery voltage. If it was due to data bit spacing, the cards Would go through the reader at different speeds which doesn't occur.

The motor speeding up briefly at the end of a faulty read is due to the way the HP67 microcode works.

The code evaluates the checksum before testing if the card has completed its travel through the reader. If a read error is detected, the program memory gets cleared also before testing if the card is out.

By this time the card has passed through the drive wheel which reduces the load on the motor. This effect must be outside the limits of the speed control and the motor speeds up. Shortly after, the code then tests if the card is out and because it is, turns off the motor.

cheers

Tony

Hi Tony,
Thank you for clarification on speed control and in-sights to the ROM code.
Andi