10 Aug
2019
10 Aug
'19
1:57 a.m.
-----Original Message-----
From: cctech <cctech-bounces at classiccmp.org> On Behalf Of Douglas Taylor
via cctech
Sent: 10 August 2019 05:06
To: General Discussion: On-Topic Posts <cctech at 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