Dec 8235 IC?

Pete Turnbull pete at
Thu Sep 3 04:29:56 CDT 2015

On 03/09/2015 09:05, simon wrote:
> is there a list of equivalents for DEC ic's?
> I've made a mistake in attaching our BA-8 to the PDP8/f and twisted the
> ribbon cable connecting connector C and D. some magic smoke came loose
> and there are a few chips broken . :-(


I don't have a list, but I do have a copy of the 1976 Signetics ICs 
databook, which lists a lot of 82xx logic.  I've not checked one of my 
M8330 boards but I guess that's what you need.

8235 is a quad (4-bit) 2-input multiplexer - with a twist.  It has open 
collector outputs and two control inputs.  The twist is that one of each 
pair of inputs is non-inverting, the other is inverting, and the idea is 
that by tying the two inputs together you can use the control inputs to 
make the outputs the TRUE or COMPLEMENT of the input data, eg to feed to 
an adder.

The data sheet is two pages, which I can scan if you want.

The An and Bn data inputs are pins 1 and 2, 6 and 5, 10 and 11, 15 and 
14; corresponding f0 to f3 outputs are pins 3, 4, 12 and 13.  S0 and S1 
are pins 9 and 7.  Vcc is pin 16, GND is 8.

Truth table:
       S0      S1      fn
      ----    ----    ----
       0       0      /An.Bn
       0       1        Bn
       1       0       /An
       1       1        1

I like the last paragraph of the description.  "The 8234 and 8235 
designs have open collector outputs which permit direct wiring to other 
open collector outputs (collector logic) to yield 'free' four-bit words. 
  As any as one hundred four bit words can be multiplexed by using up to 
fifty 8234/8235 in WIRED-AND mode."

Good thing DEC didn't go quite that far.


Pete Turnbull

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