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Thread: RTL logic circuts MC 660 and MC 672
face BY : Dan Michaels email (remove spam text)

Chris Eddy wrote:
>I have been working on some modernization efforts for the nuclear industry.
They have a number of designs which used this old logic.  The logic, if I
>recognize the numbers, are MHTL logic, which is a high threshold logic
version of DTL logic made by Motorola.  I would be wary of Dan's suggestion for
>replacing with transistor logic, Dan assumed RTL, and in reality they are a
bit more than that.  He meant well.  The best bet is to use a comparator around
>7.5V (this is fixed regardless of supply) and then deal with the logic
levels.  Outputs are either an active transistor output in a peculiar buffer
>arrangement, or a passive pullup with active pulldown.   Not a clip out
solder in solution.

According to the textbooks [if one can believe them], "all" of the
old RTL, DTL, and HTL gates are fairly straightforward NPN circuits.

So, if unable to find these gates/chips anywhere, and if fixing
the equipment as opposed to trashing it is the major consideration,
then it would seem that clip out solder in may be the only possible
course of action. It cannot be all that difficult to try, assuming
only one or a few gates are blown - either works or doesn't work.

Unsolder the old chips, solder wirewrap headers into the holes, build
a new gate on fiber board [kind with plated-thru holes], and solder to
the WW legs.

[of course, this thing probably wouldn't meet FDA approval].

- dan

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Subject (change) RTL logic circuts MC 660 and MC 672

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