On 10.09.13 20:34, Russell Brown wrote:
> Quoth andy pugh.....
> Ah...  so I can't connect pyvcp.x-minus and xhc-hb04.jog.minus-x to
> halui.jog.0.minus, without an or2, because of:
> 
> >An OUT pin can be connected only if there are no other OUT or IO pins on
> >the signal 
> 
> Which one could paraphrase as being "An IN can only have one OUT
> connected to it".
> 
> Isn't English wonderful :-)

Yup.

It's analogous to TTL or CMOS logic; what's not permitted is connecting
two OUTs together, because of contention. The two outputs will at times
have different states, but a common connection can only ever have one at
any instant.

In software logic, the only consequence is an undefined state, but in
any hardware logic family with totem-pole outputs, connecting two
contending outputs will try to short-circuit the power supply. That can
let the magic smoke out.

Erik

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