RTL Logic

From: Tom Jennings <tomj_at_wps.com>
Date: Fri Jan 7 13:19:11 2005

On Fri, 7 Jan 2005, Cini, Richard wrote:

> 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's an interesting idea. There are different types of RTL,
wanting supply voltages not +5VDC sometimes. TTL may not like
running at 6V, the magic smoke may leave. I'd use 74HC instead.
It will live at 6V.

I doubt any of them would have the same pinouts, first off. There
would be problems mapping functions (flipflops with right in/out
combinations, etc) but a few hours with a couple of databooks
would probably work that out.

You'd probably end up with little daughter boards per-chip, not
much fun to consider, but if you only need one or two it's
probably fine. It could be as little as pin swaps and a resistor
or two, or as much as two chips plus glue passives.

None of the RTL chips have much complexity, so that's a plus.


> Rich
> -----Original Message-----
> From: cctalk-bounces_at_classiccmp.org
> [mailto:cctalk-bounces_at_classiccmp.org]On Behalf Of Michael Holley
> Sent: Friday, January 07, 2005 12:08 AM
> To: cctalk_at_classiccmp.org
> Subject: RTL Logic
> I have acquired some Don Lancaster designs that use RTL logic and I am
> looking for spare parts. The MC789 hex inverter is used in all of them and I
> have 2 chips. Does anyone have a reasonable source for the MC789, I can get
> all I want for $20 a chip.
> I also have 2 MC799 buffers that are use in the Microlab. I have found two
> each of these (MC725, MC778, MC785, MC792, MC853, MC855) that I will part
> with.
> SWTPC Digital Logic Microlab
> http://www.swtpc.com/mholley/PopularElectronics/Apr1970/PE_Apr1970.htm
> Early SWTPC keyboard
> http://www.swtpc.com/mholley/PopularElectronics/Apr1974/PE_Apr1974.htm
> I think that Don Lancaster's TIC TAC TOE machine from 1971 is a very clever
> design. It uses 5 ICs and 60 diodes to play the game. I may build one.
> http://www.swtpc.com/mholley/RadioElectronics/Dec1971/RE_Dec1971.htm
> Michael Holley
> www.swtpc.com/mholley
Received on Fri Jan 07 2005 - 13:19:11 GMT

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