IBM 1800409-001A - Manual (Page 378)

Notes to the Centronics Parallel Cable Pinouts Table
Direction refers to the direction of signal flow as viewed from the
printer.
Return denotes “twisted-pair return” and is to be connected at
signal-ground level. When wiring the interface, be sure to use a
twisted-pair cable for each signal and always complete connection
on the return side. To prevent noise effectively, these cables should
be shielded and connected to the chassis of the system unit and
printer, respectively.
All interface conditions are based on TTL level. Both the rise and
fall times of each signal must be less than 0.2 microseconds.
The cable must have an overall braided shield, Belden 8345 or
equivalent.
Connectors must have shielded housings. The overall shield must
be bonded to the shielded housings at both ends of the cable.
Appendix B
B - 1 4 T e c h n i c a l S p e c i f i c a t i o n s