> -----Original Message-----
> From: cctech <cctech-boun...@classiccmp.org> On Behalf Of Douglas Taylor
> via cctech
> Sent: 10 August 2019 05:06
> To: General Discussion: On-Topic Posts <cct...@classiccmp.org>
> Subject: Pertec Interface Cable Length
>
> I have a question about cable length - any electrical engineers in the house?
Its electronics, rather than electrical engineering. Electrical Engineering is
power distribution.
>
> Connected a Qualstar 1260 tape drive to an Emulex TC02 qbus tape controller
> in a pdp-11/53. The interface is pertec with 2 50 pin cables.
>
> When I use a pair of short flat ribbon cables, 18 and 30 inches each, it
> works. Under RT11 I can INIT, Copy, DUMP, do a Directory.
>
So the hardware is good.
> It doesn't work when I use a pair of 5 foot long flat ribbon cables. Are they
> too
> long? Do I need twisted pair type of cable? Is it possibly a termination
> problem?
I can't see 5 foot being too long for data from a tape, the data rates aren't
huge. At most you have added 10ns to the delay times.
On the other hand I have been wrong in the past and could be wrong again..
I assume you have checked the cables. Ribbon cables are prone to come loose
from the IDC pins if it’s a IDC connector, and if soldered can break....
>
> Doug
>
Dave
G4UGM
