Identify ~1976 DIP40 IC marked "2501A"

[fenugrec]

Hi,
I just opened my Navtel 4950 frequency counter to see if there was any ROM that should be backed up, and I wasn't even able to ID the main processor !
It's a white ceramic DIP-40 IC with gold cap, no mfg logo , and two lines of markings :
2501A
7622

The latter is no doubt the datecode, which fits with the rest of the ICs. I'm having trouble with "2501" : the only thing I found was references to an AMD "AM2501 counter", but apparently that was a DIP24 chip (not very authoritative data; couldn't even find a datasheet). It would have been a likely candidate though : this meter is not very sophisticated; I could well believe that the display be driven directly by a BCD counter.

So, is my info on the AM2501 wrong, or is there another 70's-era IC that is a more likely fit  ?

[dexters_lab]

hmm, looks a bit intel to me, but then many of the white ceramic ICs have similar markings

if it's in a socket you could carefully remove it and look underneath, many have markings on the underside too

[leisergeist]

HP used that package a lot too back then, and they didn't usually label them very well (just internal part numbers), but probably not so in another company's device

[PA0PBZ]

No ROM or RAM, too early for a microcontroller so my guess is a dedicated counter chip.

[floobydust]

My guess AMI (American Microsystems Inc.) S2501
It's not in my '77 shortform though.

[Kjelt]

Perhaps a Signetics 2500 MOS series?

But An 2501 from 1972 is a full decoded 256 bit SRAM, does not need 40 pins, besides no battery.

Next step: trace and id the pins, vcc and gnd and inputs vs ouputs should be less than an hour work.

https://archive.org/stream/bitsavers_signeticsdcsMOS_10148267/1972_Signetics_MOS_djvu.txt

[fenugrec]

Thanks for the replies!

No ROM or RAM, too early for a microcontroller so my guess is a dedicated counter chip.

That's also my thought process at this point. I thought maybe some 8008 variants had builtin ROM but probably not that early; plus I doubt Navtel was big enough to have a custom LSI made -- I have unit serial # 0300, and the internet knows nothing about these.

My guess AMI (American Microsystems Inc.) S2501
It's not in my '77 shortform though.

Interesting, what is that IC ?

if it's in a socket you could carefully remove it and look underneath, many have markings on the underside too

Good point, but at this point I don't feel brave enough to attempt that. I think we've pretty much determined it's unlikely to contain externally-readable ROM, and if it's a custom ASIC then there's nothing I can do to make a backup.

I'd love to find a datasheet for that AMD AM2501 counter, but I'm finding nothing - just the same, copy-pasted historical description everywhere.

[Kjelt]

This unit is from 1977, a 8048/8748 could be possible (1976) however no oscillator/crystal so probably no uC.

[SeanB]

Not in my Advanced Micro Devices Schottky databook either, though they do have some multipliers in there (25S05) that are 24 pin devices

[duak]

It took a bit to find but AMD did make an AM2501 which is a 4-bit synchronous counter that came in either a 16 pin or 24 pin package.  It's in the 1974 data book which is on the bitsavers.org website.

Is the instrument made in Canada?  I see the transformer has a CSA logo on it without a corresponding UL mark.  I also see that the crystal oscillator was made in Canada.  Navtel might still be in business - I see there used to be a Navtel Communications that started up in 1975-6.  It was bought up sometimes in the mid to late 2000s.

Mostek made the MK50395 6 decade counter chip in a 40 pin DIP.  I have one from 1976 but the marking has worn off.  Toshiba apparently 2nd sourced it as the TC5070.  Perhaps someone else also 2nd sourced it.  Does the chip have 10 - 15 V on pin 1 or 22?

Mitel was a Canadian semiconductor house that had some fairly advanced processes and made all sorts of stuff but not much of their documentation made it to the web.

Cheers,

[justanothercanuck]

this is a long shot, but some early z80's had ceramic dip40 packages and were available in '76.

is there anything in the holes for the dip24 to the left of the mystery chip?  could be an upside down socket...

[fenugrec]

It took a bit to find but AMD did make an AM2501 which is a 4-bit synchronous counter that came in either a 16 pin or 24 pin package.  It's in the 1974 data book

Ah, hadn't looked in that databook. Yeah, DIP24, so that's probably not it.

Is the instrument made in Canada?

Correct - but the company that bought them don't know anything about those old units. I called them up at some point and eventually spoke to someone that actually knew the name "Navtel" but not much besides.

  Perhaps someone else also 2nd sourced it.  Does the chip have 10 - 15 V on pin 1 or 22?

Good question, I'll have to check.

But I doubt it's a Z80, it doesn't seem like those would've been available as mask-ROM parts in 75, and there is certainly no ROM inside this unit (the empty DIP socket just below is for the display panel connector)

[duak]

I'd never heard of Navtel till now.  I'm interested in Canadian high tech having been involved in it for the past 40 odd years.  What are the specs on the counter?  Could you post more pictures of it?  From what I see of it, it doesn't look badly constructed.

It's neither here nor there but should the big chip kick it, I'd bet it wouldn't be all that difficult to put an FPGA or EPLD on a header to replace it.

Cheers

[fenugrec]

What are the specs on the counter?

I don't have tons of data on this unit either, beyond what's on the front and rear panels. Channel A is 0-80MHz, channel B goes up to 1.2GHz thanks to an "Optimax CA1048" divider module - pretty cool for mid-70s gear. Rear panel has provisions for internal / external 10Mhz connections, and that's about it. I'll post some photos in a few weeks.