"Arie de Muynck" wrote:
I do remember it. I saw it inside a TTL EXOR circuit, maybe the 7486.
Two NPN's, E and B cross connected to open collector drivers (A and B),
output taken from connected collectors, with a pull-up.
At least it is symmetrical, but maybe not too fast.


A ---- E1 -- B2 pull-up
|
C1 -- C2 --+--- OUT

B ---- B1 -- E2


And of course it needed some pull-ups on the O.C. drivers as well...

pull-up
|
A --+-- E1 -- B2 pull-up
|
pull-up C1 -- C2 --+--- OUT
|
B --+-- B1 -- E2


Arie