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SHM-B ASYNC
computing equipment for consistency.
3. Wire the SHM-B units back-to-back, eliminating the
twisted-pair; see if you still have errors.
• If you do have errors, then test each SHM
individually in the following way: loopback one
SHM’s Transmit-to-Receive by using two short
pieces of wire. Connect that SHM to a dumb
terminal and key in characters; look for a good
loopback. A good loopback verifies a SHM-B in
proper working condition.
• If you don’t have errors, you have verified a
problem with the twisted-pair cable.
SYMPTOM: Occasional data errors.
1. The transmission distance/bps data rate capability
rate may have been exceeded. Refer to Chapter 1 for
information about valid data transmission distances
and bps rates.
2. There is a poor quality loop (four-wire circuit). Try
using a different four-wire circuit, or rewire the
existing circuit.