Clear a Checksum Error with a Power Up Reset

The 7921, 7922, 7931 and 7932 counters use an EEPROM to save programming details and count data. This operates by detecting the internal power supply. When the power is switched off, the internal power supply drops in voltage and this is detected. The processor halts operation and sales all data to the EEPROM. A checksum is also calculated and saved to the EEPROM.

On power up, the unit reads the contents of the EEPROM, calculates the checksum, and compares it to the saved checksum. If the calculated and saved checksums differ, the unit recognizes that a memory corruption has occurred and displays ERR CH to show a checksum error.

Usually the cause of a checksum error is either a genuine fault with the processor or EEPROM, or noise or spikes on the power supply. Noise and spikes can be reduced by fitting a mains filter. To clear the checksum error, perform a Power Up Reset using the steps below:

1. Switch off power
2. Press the PROG key and digit 5 key (keep both keys pressed)
3. Switch power on while keeping both keys pressed for 15 seconds

The memory should now be cleared to default values and settings. Re-program the unit with your configuration.