Unknown TI logic series

Tony Duell ard at p850ug1.demon.co.uk
Sat Dec 18 13:03:10 CST 2010


> >  we've had a look inside our IME 122 calculator and discovered that it 
> > is full of SN14xx logic ICs. They are mainly from TI, but there are 
> > also some from Motorola and others. It seems that they have the same 
> > function and pinout as the SN74xx parts but there must be a difference 
> > since the machine has quite a lot of SN1401 (the SN7401 is a quad 
> > open-collector NAND), but there are no pullup resistors anywhere!
> >  Some of the types are SN1400, SN1401, SN1474, SN1490; the ALU is made up
> > of SN1482 and SN1483.
> >  Anyone knows this series? BTW the supply voltage is 5V.
> >
> > Christian
> >
> TI and others often produced "House Numbers" for companies that wanted 
> to hide the 'real' part numbers of components. I would assume this is 
> what you have here. Thus the SN1474 may not be a flip-flop (7474) as a 
> result...they may well have jumbled the numbers around to make it 
> difficult to copy the circuit.

I assume everyone now realises how pointless this is. Given working 
examples of TTL chips, particularly in a circuit where you can indentify 
the power and ground pins, it is next-to-triival to work out what they 
are. I've done it many times to deal with those idiots who think that 
scratching the numbers of standard ICs (and not just TTL) will somehow 
make it more difficult to work out what is going on. It doesn't!

However, house nunbers do have sensible uses too. Perhaps the IC eas 
selected for some parameter. Perhaps it went through more testing. I've 
even met a case where several different ICs got the same house number. 
They were, IIRC, op-amps, and the point was that any of them would work 
in the circuits that specified that particular house number. I guess 
whichever was cheapeast at the time was used. And it meant that the 
production people didn't have to worry about what to fit. If it had the 
right house number on the package, it would work.

One thing I do find curious about the origianl post is that the ALU is 
made of 1482s and 1483s. As I am sure you are aware, the 7482 and 7483 
are adders, and would be logical (groan!) choices in an ALU (althoguh 
I've got a TTL-based calculator here that doesn't use any adder or ALU 
chip...). Perhaps I am reading too much into the numbners, though.

I guess the OP doesn;'t want to desolder any of the ICs. I probsbly 
would, and then carefully experiment wtih them on a breadboard.

-tony



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