Funny TTL pinouts (was Deck of IBM PLAYING CARDS)
jcwren at jcwren.com
Sun Dec 18 09:16:14 CST 2005
The "funny" pinouts actually make more sense than the corner pins
currently used, from a die bond-out perspective. Using the middle pins
results in the shortest and lowest impedance path from pin to power or
ground plane on the die. As I recall, most ECL logic uses this, for
exactly that reason. It makes PCB layout more difficult when only 2
layers are used, but for 4 layers it has little to no impact.
Tim Shoppa wrote:
>I think the funny Vcc/Gnd pinouts (often 4 and 10) were actually thought
>to be good for some reason in some specialized PCB designs - I think
>I see these show up on some early MSI quad latches (7475) and counters
>(7490, actually pins 5 and 10). I don't know if these were cross-incoprorated
>from parts that started out at Motorola or Fairchild or National or what.
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