4 • Wiring Types 026-1727 Rev 3
3 The MODBUS Network
Although the DAC can operate as a stand-alone
controller, it relies on an E2 unit for advanced features
such as remote dial-in/dial-out, logging, and alarm
control. The DAC uses an RS485 network connection
to communicate with E2 site controllers.
3.1. Wiring Types
Retail Solutions specs Belden #8761 shielded
twisted pair cables for use as MODBUS wiring (or
Belden #82761 and Belden #88761 for plenum
installations).
If the recommended cable is not available in your
area, be sure the wiring meets or exceeds the
following specs:
3.1.1. Daisy Chains
Connect the MODBUS network cable to the three-
terminal connector on the E2 COM port you wish to
assign as MODBUS. Reverse the polarity of +/- on
the RS485 cable between the E2 and the DAC.
Shielded?
Yes
Conductor Type
Twisted Pair
Gauge
18 - 24 AWG
Capacitance between
signal wires
31 pF/ft or less
(9.45 m) or less
Capacitance between
signal and shield
59 pF/ft or less
(17.98 m) or less
Nominal Impedance
12050
Figure 3-1 - MODBUS Networking
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