TTL HEX LED driver chip
ard at p850ug1.demon.co.uk
Fri Oct 29 16:38:18 CDT 2010
> I did the same thing, a '247, along with a '138 1-of-8 decoder to
> decode the high values, feeding a bunch of NAND gates. Use the blanking
> input on the 247 to disable it when A-F is being displayed. Did you
> avoid the use of the 1-of-8 decoder?
> I expect Tony's solution was 7 16-to-1 muxes, essentially a hardwired
Indeed it was... That's always a brute-force solution.
Anoyther idea. A '247 to get the 0-9 patterns. 3 off '253 dual 4-input
mexes. These decode the low 3 bits (and may need an extra inverter) to
get the segment aptters of the a,b,c,d,f segmetns of the A-F patterns (e
and g are always on in those states. And a little bit of logic to disable
the '247, enable the muxes and turn on e,g for the appropriat input
states. Probably only a couple more chips.
> There would be another solution with a 1-of-16 decoder feeding 7 NAND
> gates, doable in 8 packages (1 24-pin).
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