Installation guide

2.1.2 Pin 1 (Frame Ground) to Signal Ground
Where D-type connectors are provided on the rear panel(s) for V.24 and
X.21 interfaces, Pin 1 (Frame Ground) is connected to Signal ground
through the use of a shorting link (0R resistor). However Pin 1 is not
normally connected in Cray specified cables. If you are using alternative
cables you should seek expert advice, to avoid problems caused by earth-
loops created through connections to Pin 1.
Where it is not possible to isolate this connection at any other point in the
system, you may remove the relevant resistors. Identify the appropriate
port(s) and determine what type of interface card is fitted:
PIM-1, X890-605611, V.24 DTE, 25-way D-types R1 & R3
PIM-2, X890-605711, X.21 DTE, 15-way D-types R1 & R3
PIM-3, X890-605811, V.35 DTE, 25-way D-types No Facility
PIM-4, X890-605911, X.21 DCE, 15-way D-types R1 & R3
PIM-5, X890-607311, V.24 DTE, 25-way D-types R1 & R3
PIM-6, X890-607211, X.21 DTE/DCE, 15-way
D-types R4 & R6
PIM-7, X890-607111, V.24 DTE/X.21 DTE,
25/15-way D-types R2 & R7
X870-300451 Issue 2 2-2 Rev.0