Mullard & TI ICs marked with letters.

[factory]

I've been looking through some of the parts I acquired last month for some ICs, the lot included some marked with just one or two letters, they are branded Mullard or Texas Instruments, trouble is I can't seem to find any reference to these anywhere, can anyone help identify what they are.

David

[saddlestone-man]

They look like markings added by the design company / PCB manufacturer to stop the design from being reverse engineered.

best regards ... Stef

[TonyDuell]

ICL used markings like that at one point, I came across them on the Disk Interface Board of a PERQ2T1 computer.

[elanman99]

I remember buying 74 series TTL chips from New Cross Radio in Manchester (in the 70's) and recall getting a photocopy of hand drawn list of equivalents. I still have some 'A', and 'H' IC's (and possibly the sheet of paper). From memory I think the A is a quad NAND.

I know that the range included a 7490 because I built a Nixie clock.

I will see if I can find the equivalents list

Ian

[Buzby123]

Originally Posted by elanman99

I remember buying 74 series TTL chips from New Cross Radio in Manchester (in the 70's) and recall getting a photocopy of hand drawn list of equivalents.

I had some 'lettered' TTL, probably from New Cross in the 70's as well. Can't remember where the crib sheet went, or the chips either.

[MotorBikeLes]

I thought ICL as soon as I saw the photos.
my understanding is that any "leftovers" may have been given to the ICL club (staff into computer projects at home I would guess), so lists were common to club members. I sold a travelling wave plug in for an HP scope to such a member. I think it was a 500MHz mainframe and could accommodate a Y amp on LHS and a T/B on RHS
Anyhow, he gave me a copy of the list, and I have i5t here. eg, the A is a 7400, the the D is a 7474 etc.
I will not try to scan it here, it has rather faded. Instead I will wait to see if somebody else has a better version. If not, I will try to find time to copy it out manually if it is in obvious demand. It is laid out with about 10 columns, each line giving the basic number (7404 for example, and successive columns the 74S04, 74LS04, 74H04 plus description of functions, so not a trivial task to transcribe.
Les.

[factory]

Thank you for the info, I'm guessing they might have come from the same source, I bought them from the Stoke radio club stall at the last sale I went to, there were some with no markings that I didn't bring home.

I was rather hoping some of the letter ICs some would be DTL, but TTL are still useful for repairing my old test gear, here is all the types I have, probably don't need a list of functions, easy enough to find that info from the TI TTL databook, which is probably on the web somewhere too. Guessing the X is one of the variants (S, LS, H etc).

A 7400, AX
B
CX
D 7474, DX
F, FX
GX
H
K
U, UX

Very tempted to take a few to work tomorrow and see if the old IC programmer can correctly identify them, now I know they are TTL.

P.S. probably should have asked what the Motorola 256 ones are too.

David

[saddlestone-man]

The 256 could be a 74256, a TTL 256x1bit RAM. At Plessey Telecoms in the mid-1970s we designed them into System X. They were state-of-the-art high speed RAM at the time, and got rather hot.

I guess the question remains as to why ICL overstamped these markings onto the devices?

best regards ... Stef

[factory]

Thanks Stef, will see if the old programmer at work has a RAM test and try one next time.
The markings no different to HP or Tek putting their own codes on standard parts, but in those cases the manuals had the information to work out what they are, or gave the standard number in the parts list.

Well the IC programmer can only identify the gate type, it can't tell which output type they are, guess I can check if they are open collector types with a DMM.

A (confirmed as 7400) & AX both gave 00,03,24,26,37,38,132 as matches, Quad 2-Input NAND gates.

B & GX gave 13,18,20,22,40,140 as possible matches, Dual 4-Input NAND gates.

D (confirmed as 7474) & DX both gave 74, Dual D-Type Flip Flops.

F & FX both gave 30, 8-Input NAND gate.

H gave 02,28,33,128 as possible matches, Quad 2-Input NOR gates, 128 is a line driver.

U & UX gave 10 & 12. Triple 3-Input NAND gates.

CX & K were both unknown devices, not all devices are supported by the old programmer.

David

[MotorBikeLes]

I said I would try to transcribe my blurred copy of the ICL numbers, which is now completed. However, before I do, can I have a couple of PRECISE answers.
Consider Octal Buffer Tri-State and Octal Driver 3 State.
Are Tri-State and 3 State as in the above synonymous, and if so, which is more appropriate?

I assume O/C means Open Collector, but which is preferable, O/C, O-C or OC?
No doubt somebody will say it does not matter, but I understand such terms can be part of "Statements", in which case I think is DOES matter.
Regards, Les.

[TonyDuell]

IIRC 'Tristate' was a trademark of one of the IC manufacturers (National Semiconductor?) at one time, but is now pretty much universal.

[factory]

Even Texas Instruments can't agree, the older TTL (aka TTL Vol 1) databook lists them in full in the functional index. The later TTL Vol 2 (AS,ALS) databook has a header for "type of output", with 2-State, 3-State & OC listed, but the 228 FIFO has Open Coll. instead.

I would go with the shorter 2-State, 3-State & OC myself.

David

[MotorBikeLes]

OK, answers not as definitive as I hoped, so we settle for my interpretation.
My interpretation of the equivalents in PDF formal.
I think I succeeded in reading it all, but the way it had been laid out was confusing. i trust I have interpreted it all correctly.
If anybody spots any "glarers", or even just subtle ones, let me know and corrections are possible.
Les.