DZ11 EIA dist panel on eBait

[Paul Koning]

> On Jun 30, 2020, at 12:19 PM, Tony Duell via cctalk <cctalk at classiccmp.org> wrote:
> 
> On Tue, Jun 30, 2020 at 5:15 PM ed--- via cctalk <cctalk at classiccmp.org> wrote:
> 
>>>> Connecting a DZ11 directly to the pcb with the connectors won't work directly as expected.
>>> 
>>> Why not? I've linked up DZ11s to the distribution panel PCB with a
>>> straight ribbon cable and had no problems.
>>> 
>>> The RFI filters effectively swap odd and even pins in the cable (the
>>> pins are straight through the filter but of course you look at them
>>> from opposite sides). That's why the short ribbon cables between the
>>> filters and the distribution panel are not straight through but have
>>> crossover connections.. But if you remove both the filter and the
>>> crossover cable it will work as you expect.
>>> 
>>> -tony
>> 
>> Ah, I did not know that, interesting to know.
> 
> I suspect the filters were a later addition. The original idea was to
> just connect the DZ11 PCB to the distribution PCB with a
> straight-through cable. But the filters had to be added to meet some
> interference regulations (is that fcc part 15??), the filters swapped
> the pins over, hence the special crossover cables between the filters
> and the distribution PCB.

That sounds right.  Yes, FCC part 15.  That arrived somewhere in the middle of the PDP-11 era, so old PDP-11 peripherals and systems don't comply while later ones do.

	paul