New subject: 74189s and 74170s and ALUs, etc.

2 Nov 2001

From: Ben Franchuk &lt;bfranchuk(a)jetnet.ab.ca&gt;
...

  The 74289 is also the same part/pinout save for
instead of open collector
 they are tristate outputs. 
OK I would have used a generic 16x4 non inverting memory. 

The 74189 is inverting, though adding an external inverting buffer is NBD.
If y
ou want a part that wasn't inverting then you have to use the 4x4 register
file (74170) times for to get nearly the same thing.  The 4x4 however
allowed
was a two port device.

...
 > The 74382 is not an ALU, it's a carry look
ahead generator.  The 74381 is an
...
   ALU. 
I have a 74F382 data sheet -- this is a ALU. 

Really, my TI databooks have it as the lookahead carry generator for the 381
ALU.

...
   BZZZT!!!  By
ealy 1980 the 2901 was already passe', as were TTL cpus.
 I presume by that you really meant early (very early) 1970s as the 2901
 is a 1970s part. 
That is hard to say what era my cpu is from as I have to fake it from
what
I would of built in 1980's. LS TTL was just becoming popular. 8 bit
micros
where the big thing.I used a PDP8/e and a PDP8/S in 1983. 

Your still off by at least 5 years.  1976 is more the LS ttl era.  By early
1980s the designs for CPUs were going to gate arrays.

...
   Also the 2901
is directly traceable to 74181, 74189 like parts. 
The 2901 is a nice bit slice chip. If I had used it in my alu I would
have
fewer states per instruction, but then I would have needed to go to
micro-code style architecture. This design was random logic where
no PROMS need ever be programed. 
That was late 60s very early 70s design.   By late 70s microcode was common
or at least state machines.    The availability of bit slices by the early
70s influenced
this greatly.

...
  I already have
a real PDP-8. ;) 
I should have known :) 

;-)

Allison

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