Question on chip date code

From: Eric Smith <eric_at_brouhaha.com>
Date: Mon Feb 10 13:09:00 2003

Sellam wrote:
> I am looking at a chip that is causing me confusing with regards to its
> actual date code.
>
> The chip is labeled thusly:
>
> (logo) /718
> DM74157N
> 9322
>
> (logo) looks something like this: /\/
> /\/
>
> ...which probably makes it National Semiconductor.

Yes. The "DM" prefix is also indicative of that. Most other vendors
of 7400 series parts copied the "SN" prefix from TI.

> My first instinct is to guess that its date code is 9322. However, it
> does not fit within the context of the rest of the board, which is 1976.

The DM74157N was also known as a DM9322, so the part is dual-marked.

> They are definitely not original, as the board calls for a 74257 but the
> 74157 has been put in its place with the addition of a capacitor across
> +5 and ground.

The capacitor is just for additional decoupling, and doesn't change
the function of the chip. The particular board you're looking at (I
can guess what it is) was spec'd for either a 74157 or 74257.

Eric
Received on Mon Feb 10 2003 - 13:09:00 GMT