Manufacturer:  Hewlett-Packard Model:  5216A Year:  1967 Schematic:  RE

Max. Rate:  12.5 MHz Display:  NIXIE Digits:  7 Logic:  TTL

An early all-IC counter. The main ICs used in this counter are MSI TTL decade counters and NIXIE drivers. They are proprietary HP devices having some additional functionality not found in the standard 7490 / 7441 devices.

The additional functionality of the ICs is for leading-zero blanking in the display. The decade counter ICs have an 11th state (decimal 15) to represent blanked-zero. The NIXIE driver IC blanks the NIXIE upon input of 15. Upon reset the decade counters are set to the blanked-zero state. Any clock activity on a given decade (digit) unblanks that decade. At the end of the gate/count period leading zeroes are still blanked while lower-order zeroes have been unblanked. This scheme can result in some briefly idiosyncratic displays when changing the function mode.

Unfortunately the special ICs seem to fail somewhat frequently, especially the NIXIE drivers, making it difficult to keep units of this model or series functional.