Identifying mystery TI ICs (Motorola MDP-1000 investigation continues...)

Josh Dersch derschjo at
Sun Oct 4 13:42:17 CDT 2020

On Sun, Oct 4, 2020 at 10:26 AM Brent Hilpert via cctalk <
cctalk at> wrote:

> On 2020-Oct-04, at 1:22 AM, Josh Dersch via cctalk wrote:
> > More mysteries while poking at the MDP-1000.  Spent some time this
> evening
> > working out the rest of the signals on the power harness (I suspect
> inputs
> > for an LTC circuit and a "power good" signal, as well as something
> > connected to a relay on the backplane, probably related to power
> control).
> >
> > There are a lot of unidentifiable ICs on the main CPU logic board and on
> > the backplane, mixed in with bog-standard 7400-series TTL.  Curious if
> > anyone has any ideas, as my searches and perusal of datasheets/databooks
> on
> > Bitsavers have turned up nothing.  These are all TI-manufactured ICs,
> 1969
> > manufacturing dates, with "SN48xx" and "SN63xx" part numbers (a few omit
> > the "SN" prefix.)  I'm wondering if these are just standard 7400 ICs with
> > special codes; for example there are several SN4816's near the edge
> > connector for the I/O bus, where a 7416 might (?) make sense, and from
> some
> > basic probing and following traces I think the pinouts make sense.
> > (Everything's conformal coated so it's a real bear to beep things out...)
> >
> > Any ideas?
> I have run across TI ICs from that era with odd/unknown series numbering,
> in particular the SN3900 and SN4500 DTL ICs.
> Notably:
>         - by pinout they match up with standard DTL series ICs,
>         - I have only found these in equipment from one manufacturer:
> calculators built by Canon.
> I received a solitary page of datasheet for some of them (by way of a
> Canon service center many years ago), but I have never seen them mentioned
> in TI databooks from the era, even in those sections where they list e.g.
> "other products from TI" and proceed to list little known series and part
> numbers.
> So an obvious guess is these were house numbering systems of standard
> parts done for the purchaser/equipment manufacturer but with TI's format
> scheme rather than a format specified by the manufacturer. Another guess
> would be standard parts tested and selected for purchaser-specified
> parameters, although that seems a little excessive for these cases.

Yeah, either of those options seems a likely possibility.  It definitely
seems like they were building this thing for bulletproof operation, so
maybe it really is the latter.

> The 54/7400 series originated with TI in 65, I'm not aware of them
> producing any other TTL series, other than perhaps second-sourcing some
> other manufacturer's.
> I guess that's another possibility - another manuf's TTL series, labeled
> differently.
> Odd that this Motorola CPU is filled with ICs manufactured by TI.

Yeah, the irony of this was not lost on me.  Other than the aforementioned
linear ICs in the core modules, every IC in this has a TI logo on it.

> It's conceivable, although it seems less probable, that they're DTL rather
> than TTL.
> On the whole, best guess would seem to be 7400-series inside.

Yeah, I'm guessing (hoping) 7400 as well, especially since there are actual
74xx-labeled ICs in here casually mixed with the 48xx and 63xx.

A thought occurred, that if I get desperate I could remove a few of the ICs
and attempt identification using the IC tester I have.  Not going to do
that unless I can't figure it out any other way.  The good news is there
aren't too many varieties.  I haven't done a full inventory but there's not
more than a dozen or so different types in here.

> --
> On another issue, did you trace the +/-15V lines to the core
> address/inhibit drivers?
> Could some of the remaining wires from the PS be other core supplies - 15V
> was a little low compared to most core systems I've seen.
I did manage to trace the +/-15V lines to the drivers on the core memory.
I don't believe any of the extra signals are other voltages -- three of
them go to the CPU board, one goes to the aforementioned mystery relay, one
goes to a tiny bit of logic on the mainboard (I suspect some manner of
LTC), and the last goes to a trace that just dead-ends and goes nowhere at
all.  The very little documentation I have on the CPU itself suggests that
the supply provided only +5 and +/-15.  There are two sets of power rails
for each; the first goes to the CPU, front panel, and two memory slots, the
second set goes to the other two memory slots.  I suspect that upgrading
past 8K of memory required a power supply upgrade.

- Josh

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