Re: VIC-20 "all games in one" cartridge update

From: john/lori (
Date: 2001-04-01 22:03:52

I thought I might add that I wouldn't really expect latch up to be a

But it occurs to me that I'm assuming you understand that the protection
network generally clamps the input and output pins with diodes, in some
fashion, to VCC and ground, so if eg you apply +5 to a pin, you'll be
trying to pull VCC towards +5V through a diode drop and depending on the
details of your 3.3V supply and what kind of load you've got on the 3.3V
line, you might well succeed.

But then too, I'm not very familiar with the LV families, that may not
to them.

> Are you familiar with latchup?
> Parasitic SCRs that switch on and short the device under certain
> conditions
> (like when the protection diodes are passing enough current).
> I don't know how much of a problem this might be in modern devices,
> especially
> ones designed to operate in mixed voltage environments.
> I note that that link you posted say "latchup performance exceeds 300ma"
> not sure what that means, either that you must inject >300ma to cause
> latchup,
> or the SCR holding current exceeds 300ma (I'm guessing)
> I also note that it says "do not force a signal on an I/O pin when it is
> an
> active output, damage may occur" I suspect trying to drive a 5V line
> would be included there.
> I know I've read several app notes on the subject, I'll see if I can
> find them,
> if you're interested.  (not sure if they were on line or in an
> electronic form)

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