Robertshaw Smart Sense Series Installation Manual page 46

In many cases where multiple thermostats are used in a single network or on a
long network run, the two place DIP switch located between the R and R/Com
terminals on the thermostat circuit board should be switched ON to improve
network reliability.
It is essential that the network be wired as a daisy chain as show in Figure 26.
Figure 27 and Figure 28 show examples of how NOT to wire a ModBus network.
ModBus
Master
SMART 2000 SMART 2000 SMART 2000 SMART 2000
Figure 26 Correct Wiring
SMART 2000
SMART 2000
SMART 2000
ModBus
ModBus
Master
Master
SMART 2000
SMART 2000 SMART 2000 SMART 2000
SMART 2000
Figure 27 Incorrect Wiring Figure 28 Incorrect Wiring
18 gauge (1 mm) twisted pair unshielded wire can be used for short
communication runs.However, for longer runs or where electrial noise may be
present, a shielded twisted pair should be used.
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