> > <A _lot_ of calcultors had a multiplexed nixie tube display. It was
> >much less common in test gear which is why I guess you've not seen it.
> >
> > Really, never saw many that did, the vacuum florescent (bluegreen)
> > were generally mux'ed..
>
> Maybe I wasn't being very clear. What I meant was that many of the
> calculators that used nixie tubes multiplexed them. Direct drive of
> nixie tubes in calculators is very rare (I can't think of an
> example off the top of my head).
>
Some early electronic calculators did use directly driven Nixies that
were not multiplexed. Two examples:
The Sumlock Anita C/VIII (Mark 8). Each Nixie was on a 'daughter' board
with a 10-stage ring-counter (implemented with Thyratron tubes) that
directly drove each 'digit' inside the Nixie.
(See
http://www.geocities.com/oldcalculators/anitaC-VIII.html
Another example is the Sharp Compet 20 (Sharp's second electronic
calculator). Each 'digit' card has a 4-bit shift register implemented
with discrete transistor flip-flops that the BCD digit is shifted into.
Along with the shift register, there is gating logic and driver transistors
to convert the BCD digit in the register into a 1-of-10
to drive the Nixie.
(See
http://www.geocities.com/oldcalculators/comp20.html
By the late 1960's, most Nixie calculators used multiplexing to reduce
the complexity of the circuitry. Most machines used a bit-serial
ALU anyway, and the main registers were made up of shift registers or
bits circulating in an acoustic delay line, or bits in a core stack,
and simply 'scanning' through each digit was a normal part of the
operation of the machine anyway, so the multiplexing was almost
'free' in terms of the additional logic needed to run the display.
Rick Bensene
The Old Calculators Web Museum
http://www.geocities.com/oldcalculators
Received on Sat Oct 23 1999 - 23:45:33 BST