Unknown TI logic series
rickb at bensene.com
Sun Dec 19 11:53:07 CST 2010
While this posting doesn't address the SN14xx-chips the original poster
queried about, there is another machine that I have that has some
TI-made SN12xx chips that I was able to find the story of that may be of
interest to others.
The Friden 115x (Printing) and 116x (CRT Display) calculators use three
interesting TI chips that have SN12xx part numbers that I know to be
custom chips made for Singer by TI.
The Friden 130/132 calculators, the predecessors to the 115x/116x lines,
didn't have adders in the classic sense. These machines are all based
on counters. The original architecture of the EC-130 was based on a
series of four five-bit counters that were interconnected in different
ways (by mostly gating logic) to allow them, by counting up and down, to
perform the math operations. After the 130 was introduced, in the
process of developing the EC-132 (which added square root), it was
realized that all of the functionality could be done with three counters
rather than four, and a rework was done of the EC-130 boardsets to use
this realization to reduce the part count, and thus the manufacturing
cost. A few EC-132's were also made with the four-counter architecture,
but soon into production the EC-132 was also changed to the
three-counter design. Each of the three counters had a slightly
different logic design.
The goal of the 115x/116x calculators was basically to shrink the
machines down by using IC logic rather than discrete transistors.
These machines were implemented using a mix of small-scale DTL and TTL
devices. Friden didn't seem picky about vendor...there are chips made
by Signetics (7400-series TTL), Motorola (MC8xx DTL), TI (7400-Series
TTL, SN158xx DTL) all in 14 & 16-pin plastic DIPs.
Along with all the SSI devices, there are three 24-pin MSI devices, part
number SN1286, SN1287, and SN1288. These chips, which were custom made
for Friden by TI (this is mentioned in discussions I've had with one of
the engineers that worked on the development of the machines), implement
the three counters.
Is it possible that the SX12xx-series TI part numbers were for custom
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