TTL HEX LED driver chip

[Tony Duell]

> 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 
> ROM.

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).

Yep.

-tony