12 Dec
2010
12 Dec
'10
12:05 p.m.
Brent wrote:
On 2010 Dec 10, at 2:36 AM, Christian Corti wrote:
>
> we've had a look inside our IME 122 calculator and discovered that it
> is full of SN14xx logic ICs. They are mainly from TI, but there are
> also some from Motorola and others. It seems that they have the same
> function and pinout as the SN74xx parts but there must be a difference
> since the machine has quite a lot of SN1401 (the SN7401 is a quad
> open-collector NAND), but there are no pullup resistors anywhere!
> Some of the types are SN1400, SN1401, SN1474, SN1490; the ALU is made
> up
> of SN1482 and SN1483.
> Anyone knows this series? BTW the supply voltage is 5V.
I can't find a reference for those numbers, and I
haven't seen them
before, however I have seen TI inexplicably producing series identical
or similar to more-common series, but numbered differently. For
example, the SN3900 and SN4500 series are very similar to more-common
DTL series such as the 700/800/900 series, but I have never seen a
reference for the 3900 or 4500 series in TI databooks. One suggestion
might be they were a 'consumer-grade' series, a step below the standard
commercial-grade stuff.
Remember this was the late 60's or early 70's, and the thought of 7400 as the
"super series" with variants like 74L00, 74H00, 74S00 actually being inside the
family had not quite taken over in the same sense that it did later,
even inside TI. I don't think it's so much that the
SN1400's/SN3900's/SN4500's
were a step below commercial grade, but they probably had product-specific
fanin/fanout/noise/current constraints and maybe even custom pinouts
or built-in pullup variants in their specs.
The 7400 "super series" of pin compatible parts in different
speed/current/fanout
levels organized by 74L00, 74H00, 74S00, 74LS00 with often identical pinouts
was truly genius from a marketing-meets-technology point of view.
Not too different than say the 9-pin dual triode with similar to
identical pinouts but different gain variants (e.g. 12AU7/12AT7/12AX7) and a zillion
commercial/aerospace/computer variants (e.g. 5814A, 5963, etc.)
With regards to pinouts not everyone even inside a company had the same thoughts
regarding pin locations for Vcc and gnd. TI did a pretty good job most of the time
putting
them at 7 and 14 or 8 and 16 for TTL which did simplify layout, but there are lots of
exceptions
even inside the TTL product space. And sometimes there were good reasons for the
exceptions, other times I think it was just internal squabbling :-)
You can see some of this playing out in TI's competitors logic families too, e.g.
Signetics
Utilogic with different subfamilies inside the Utilogic superfamily.
Tim.