Help identifying IC

Brent Hilpert bhilpert at
Sat Jan 20 21:55:13 CST 2018

The mid-70s saw a plethora of dedicated-logic LSI TOD clock chips in 24-28 and sometimes 40 pin packages.
Most prevalent IME were those made by National, Mostek and Fairchild.

Going by the labelling for the other two chips, fair chance the ID of the big chip is staring right at us: MPS 7123.
Micro Power Systems and Commodore Semiconductor Group used chip ids of the form MPSxxxx, although I have nothing for specifically MPS7123.
The former would fit the battery operation.
Try tilting the IC obliquely to the light and viewing angle if you haven't, often shows up a remnant impression of printing on the IC.

I never did see a TOD clock chip in a gold-topped package - they were generally targetted for the low-cost consumer market - although by the date code it may be early enough, in the period that consumer products would have such packages.

The clock chips were pretty straightforward but varied in options:
		generally 2 power pins
		2 oscillator pins (for the multiplexing)
		50/60hz input pin (for TOD timing if separate from internal oscillator)
		4 or 6 digit-drive pins
		7 segment-drive pins
		some setting/mode control pins which could be either switched direct to a power rail or multiplexed with isolation diodes off the digit pins
		often an AM/PM indicator pin
		alarm control output pin

(There were some for non-multiplexed display drive but that would be >28 pins.)
(Some had BCD rather than 7-seg numeral outputs)

So, yes, it's hard to say, could be a dedicated TOD clock, could be an evaluation module for something like a multi-digit decade counter IC.
Perhaps a start-stop timer, 3 switches: start / stop / reset.

Not difficult to trace out, could see if there are any other pins that might be for external connections like timing control or counter inputs.

On 2018-Jan-20, at 6:06 PM, Josh Dersch via cctalk wrote:

> Hi all --
> I picked up this little toy at VCF West last summer:
> As far as I can tell, it's supposed to be a clock and I assume it was a kit -- this one was definitely hand-assembled.  It's powered by two AA's (apparently, there are no markings), has a 4 digit LED display, and at the moment it does not work at all.
> Can't find anything about this item at all.  At the moment I'm curious what the 28-pin IC at the top is -- there are no markings of any kind anywhere on the chip.  It has an interesting construction -- blue plastic on both sides with a metal cap over the die.  The two other ICs are RCA 3081 and RCA 3082 which are simply transistor arrays for driving the 4-digit LED display.  I assume the 28-pin IC is a simple microcontroller with built-in ROM, or perhaps it's a device specifically designed to run a digital clock.  Whatever it is, I'd love to know what it does so I can debug this thing and possibly source a replacement.
> I realize this is not a lot of information to go on, but on the off-chance someone's seen something like this before I figured I'd give it a go...
> Thanks,
> Josh

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