DEC-423 to RS-232 chip?

From: Chuck McManis <cmcmanis_at_mcmanis.com>
Date: Sun Dec 31 15:56:06 2000

At 07:53 PM 12/31/00 +0000, Tony wrote:
>Are you sure you've not miscounted? I would think pin 16 goes to DB 6 and
>pins 12 and 13 to DB7.

You're right, I rechecked it from the "top" and the pins involved are 6, 7
and not 7,8.

>I think this chip is nothing more than an RFI filter. There's a filter
>network with the input/output going to pins across the chip (like 2 and
>19) and the common connection going to ground via the 4 corner pins of the
>chip. Many of the chips are R-C-R t-networks, but I think some of the
>better ones are C-L-C pi networks. No idea what yours is.

Interesting, I'm now wondering if there is someway to do this without a
chip (a few discretes perhaps).

>I've seen these 'chips' used in all sorts of devices -- the Apple Mac +
>certainly has them in series with connections to the external connectors.

No luck finding the equivalent of a "databook" on line though. Several
services to make them for you if you know the required specs :-)

>This would explain the lack of power to the chip, and the connections given.

I certainly concur here.

>The adapter should work without the 'chip' if you short pins across the
>empty space (i.e 2-19, 3-18, etc). It might not meet the FCC, etc,
>requirements on electromagnetic radiation, though.

Hmm, perhaps we'll try this out in a bit, my motivating issue is this:

         With this fancy I've-only-got-one DEC do-hicky with MMJ
         on one side and DB-25F on the other. I get 100% reliable
         serial communications with my VAX 4000/60.

         With my third party you-can-build-this-yourself MMJ to
         DE-9F wired through connection. I get into situations
         where the VAX will suddenly stop seeing anything I
         type at it. (it still seems to receive and the RxD
         path is sound electrically.

So my thought was to see what it would take to duplicate the DEC gizmo.
The other thing bouncing through my head here is the DEC-423 multiplexor
I'm going to build for the VAXStax cluster project.

--Chuck
Received on Sun Dec 31 2000 - 15:56:06 GMT