RTL Logic

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Fri Jan 7 17:55:00 2005

>
> OK, this might sound like a stupid question, but being somewhat ignorant of
> RTL logic in comparison to TTL and other designs, what, if anything, can be
> substituted for RTL logic chips?
>
> For example, if I wanted to build one of Don's devices and I wasn't
> concerned with using "vintage" chips, could I do it "plug-and-play" using
> current TTL?

It is difficult to mix RTL and TTL in the same circuit, the supply
voltage and logic levels are different.

RTL chips are slower, and have different switching characteristics to
TTL. If the devices are used as plain digital devices, and if the timing
delays are not critical, then you should be able to built one of those
circuits using entirley TTL devices. But if they use gates as oscillators
or monostables (read : If there are RC networks about), then you will
almost certainly need to make some changes.

The other thing to watch out for is that many older logic families
(certainly DTL, I suspect RTL too) had passive (resistive) pull-ups on the
outputs, and could be wire-ANDed without problems. TTL, of course cannot,
unless you use open-collector devices with an external pull-up resistor.

The bottom line : You can almost certainly make a functionally-identical
device with TTL and the changes will not be that major, but there could
well be changes, It may not be just a matter of replacing a NAND gate
with a NAND gate, etc.

-tony
Received on Fri Jan 07 2005 - 17:55:00 GMT