This is essentially a RAM. It's 4 4-bit words, and is commonly used as a
translation buffer for extending addresses, etc. I have several old S-100
memory cards of relatively large capacity and these use '170's, or '670's (the
tristate version) in order to map a given block of memory into another.
Consider, for example, a simple-minded implementation of an EMS scheme. You can
map a 16k byte region of memory into an upper block simply by using the upper
two address lines to select a 4bit address which you've loaded into the RAM
location that corresponds to the location in the '170/'670 that corresponds to
the two upper addresses. In order to write to these, it was common to map them
into I/O space for read/write, and, when they weren't accessed that way, their
output drives the addresses 16..19. One board uses two '670's to generate the
upper 8-bits of address.
Dick
----- Original Message -----
From: "Ethan Dicks" <erd_6502_at_yahoo.com>
To: <classiccmp_at_classiccmp.org>
Sent: Tuesday, October 16, 2001 10:41 AM
Subject: 74170F - 4x4 "register file" - what's it good for?
>
> I recently "helped" a friend by accepting a largeish box of discarded
> engineering samples, etc., when his employer cleaned house. In the
> box of assorted (and unsorted ;-) ICs were a quantity of 74170Fs (and
> 54170Fs. I have quite a few 54-series parts from places that spent
> big bucks for protyping supplies then threw them out later), maybe 20-30.
> Not recognizing the part number, I turned to the 'net to look them up. So
> they are a "4x4 O.C. register file"... The only thing I could think to use
> them for would be SSI/MSI microprocessor implementations. Did they have a
> typical use?
>
> One cool side effect of going through all these chips - most of them have
> date codes from 1969 - 1978. Nice for repairing vintage machines with.
>
> -ethan
>
>
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Received on Tue Oct 16 2001 - 13:48:51 BST