22
SHM-B PLUS ASYNC
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.
3. Check the path of your four-wire circuit for potential
sources of interference (fluorescent lighting,
electrical motors, etc.). Such sources of electrical
“noise” can provide an environment in which
unwanted signals are induced onto your four-wire
circuit. Also, check to see if an adjacent four-wire
cable carrying a separate data stream is creating
