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LeveLine
®
Instruction Manual
10401-01026 Rev D
6.10. MODBUS Communication Protocol
The LeveLine
®
supports the slave device side of the Modbus communication standard in
RTU and ASCII modes, and responds appropriately to commands sent to it by a Modbus
master device.
6.11. MODBUS Digital Interface Wiring
In the LeveLine
®
, Modbus is implemented over a half-duplex 3.5V RS-485 serial interface.
In this configuration, the LeveLine
®
is permanently on and Modbus data is instantly
available on request. The current drawn from the external supply by the standard LeveLine
®
Logger/Mini in this mode is less than 10mA. The -CTD versions draw less than 20mA.
Six Core Cable Usage
Core Colour
Designation
Connection
Red
Power ve
5V – 24V DC +ve power supply input
Black
Power supply –ve
Power supply ground
Blue
RS485 (-/B)
Controller RS485 (- or B) line
Green
RS485 (+/A)
Controller RS485 (+ or A) line
Yellow
SDI-12 / Modbus Select
Power ve (see note below)
White
N/A
Not used. Cut back
Screen
Screen / Shield
Power supply or chassis ground
Note:
The yellow core is used to select between SDI-12 or Modbus (RS485) serial data
communications.
The yellow core must be tied to the +ve power supply for Modbus
mode.
© 2019 Aquaread
®
Ltd.
www.aquaread.com
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