Funny TTL pinouts (was Deck of IBM PLAYING CARDS)

J.C. Wren 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. 

    --jc

Tim Shoppa wrote:

> [snip]
>
>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.
>
>Tim.
>  
>



More information about the cctalk mailing list