[sdiy] No Power 4070 ring mod??

[Magnus Danielson]

From: Ken MacBeth <macbeth2600 at yahoo.co.uk>
Subject: [sdiy] No Power 4070 ring mod??
Date: Fri, 28 Dec 2001 16:14:48 +0000 (GMT)

> I have also discovered that this 'single-gate' exor
> ringmod requires no power to the chip, similar to the
> MS20 ring mod! But why?.......

Because the input signals feeds the logic, or rather, the transistors
performing the logic.

They do this by the standard input protection diodes. For XOR logic,
you allways have one input high when you want to deliver a high
output. However, it will not work for the zeroes because on the case
of both inputs high, there is no feed of low level into the
curcuit. Thus, you must wire up the ground feed at least, but you may
drop the positive feed. Please not that this resoning is valid for XOR
gates only, and XNOR is a different story.

Do I recommend this way of doing things? No... but if you like evil
curcuit-bending this is one of the things that should be natural. Long
lines of logic lacking positive or negative feeds is not recommended,
but with some clever planning you can drop them here and there for
simpler logic. Forget it for more complex stuff (like a flip-flop)
since you end up really depend on inputs and the current drawn so that
you are bound to get eratic or failure behaviour.

One nice little feature is to drop the Vcc and ground feeds at the
assigned pins and then wire them to the inputs of a gate. But that may
be too obvious ;O) so you better just arbitrarilly use them to "lock"
certain input signals as needed by intended logic. Even more fun is it
when you use the power feeds as part of the "logic", this is a real
nasty ;O)

Cheers,
Magnus