🚀 go-pugleaf

In <1992Apr16.154345.11907@ucsu.Colorado.EDU> rainer@spot.Colorado.EDU
(Rainer Malzbender) writes:

>In article <dfs.703361967@ro> dfs@doe.carleton.ca (David F. Skoll) writes:
>>I'm using some LSTTL parts in a circuit I'm building, and some inputs
>>have to be tied to a constant logic "1".
>>
>>Why in most designs I've seen do people use
>>either the resistor or spare gate method?

>I always thought the reasoning had to do with current limiting in the event
>of a catastrophic failure by the chip containing the pull-up. Without a
>resistor you could short out the power supply, although that doesn't seem
>to be such a big deal any more. Certainly for home hacking I never use
>resistors.

I'd imagine that shorting the power supply through a chip would pretty
quickly burn the bonding wire or power metalization in the chip.

One other reason someone mentioned (that I had forgotten) was that using
a resistor makes it easy to change the value on the pin for test purposes.
That's why some designs have a logic "0" tied to the output of an inverter
whose input is tied to Vdd through a resistor... (whew.)

In summary, as William McFadden and Brian Rhodefer wrote to me, LSTTL inputs
are really DTL inputs, and don't need the resistor for protection.

--
David F. Skoll