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

Josh Dersch derschjo at
Mon Oct 5 01:13:53 CDT 2020

On Sun, Oct 4, 2020 at 11:42 AM Josh Dersch <derschjo at> wrote:

> 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

Just made a minor breakthrough; a random usenet post suggested that the
MDP-1000 was just a rebadged General Automation SPC-12, and so it is.  I
suspect the internals of the unit I have (which is badged as an "MDP-6650"
on the rear) are a bit different than either the MDP-1000 or the SPC-12
(and I'm no closer to finding answers to my IC identification questions),
but it at least gives me another avenue to explore...

(Bitsavers has a few items:

- Josh

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