19 Apr
2006
19 Apr
'06
6:59 p.m.
Tony Duell wrote:
There was a Fairchild one, I forget the number.
I used a 7447 to replace the front panel on a Nova 2 (3?).
The OC outputs fit the Nova's bus nicely. And, by a bizarre
twist of coincidence, some of the digit encodings would
perfectly match the data intended to be seen on the bus
when a certain (reduced!) set of front panel switches
were keyed. So, we could boot, step, etc. a preloaded
core image without having all of that hardware dangling
off the front of the machine.
What was more
amusing was two different versions -- "with tails" and
without! :>
There's also the 'hooked 7' (segments a,b,c,f using the conventional
names), used by some Japanese manufacturers. AFAIK no TTL decoder ever
generated that one.
In the mid 70's there were several circuits in the UK magazines to turn 7
segment code back into BCD, so you could use clock/calculator/DVM chips
with built-in display drivers in other logic circuits. Most of those
encoder circuits, of course, made liveral use of the 'don't care states'.
Some of said circuits would handle both tailed and tail-less 6's and 9's,
but IIRC most of them failed on hooked 7's.
That
said, I think it is a pity there wasn't a later TTL 7 segment
decoder chip (say a 74LS547 or something) that did display 0-F as you
might expect.
*Something* does this -- though I may have been driving LCD's
at the time (thus CMOS parts). But, I remember a
7441 (though
what I used it for I am unsure... :< )
1-of-10 decoder, commonly used to drive nixie tubes.