Xylem ADAQCPC Modbus Aquavar CPC - Manual (Page 3)

3
OVERVIEW
The Modbus ® protocol was introduced by Modicon, Inc. for use in control environments featuring Modicon
programmable controllers. Due to its ease of use and implementation, this common PLC language was quickly
adopted as a de-facto standard for integration of a wide variety of master controllers and slave devices. Modbus
is a serial, asynchronous protocol. Transactions are half-duplex, featuring a single Master controlling one or more
Slaves. While RS232 can be used for point-to-point communication between a single Master and a single Slave,
a more common implementation features a multi-drop RS485 network with a single Master controlling multiple
Slaves. The AQUAVAR CPC features RS485 for its Modbus physical interface. In all cases, the AQUAVAR CPC will
act as a slave in the network.
RTU
The Modbus specification defines two distinct transmission modes: ASCII and RTU. The AQUAVAR CPC supports
RTU only.
SETTING UP MODBUS COMMUNICATIONS
Terminated
Station Station Station
Terminated
Station
X1 Identification
28 Screen
29 B
30 A
31 AGND
32 Screen
SCR
B
A
GND
B
A
GND
SCR
28 SCR
29 B
30 A
31 AGND
32 SCR
ON ON
ON ON
RS485 Multidrop Application
Other Modbus Devices
Hardware Description 1
RS485 Interface
J2 J5 J2 J5
off position on position
Bus Termination
1 For functional descriptions, see “Standard Serial Communication” addendum.
Modbus
Connections
for each
Aquavar