Manual

131
0700015-J0 Rev B
12. Modbus® Communications Protocol
This feature enables CXC communication of alarms and live signals using Modbus protocol (messaging
structure developed by Modicon®.
A message is encoded in Remote Terminal Unit (RTU) data format and is communicated upon query via
Transmission Control Protocol (TCP) to any Modbus supervisor or master. Reference: Modbus application
protocol specification v1.1a (www.Modbus-IDA.org).
The CXC acts as a server on Ethernet networks known as Modbus TCP RTU: TCP/IP over Ethernet,
default TCP port = 502. The server is always up and running when CXC starts up; ready to respond to a
client query.
CXC communications cannot be configured as Modbus gateway, to behave as both server and client at
the same time, and does not support Modbus Plus high speed token passing network.
Modbus protocol offers service specified by function codes (see tables provided). A function code is an
element of a Modbus request/reply Protocol Data Unit (PDU). The CXC supports the following:
• 0x01 (Read Coils): Read CXC relay status bits,
• 0x02 (Read Discrete inputs): Read alarm tables status bits,
• 0x03 (Read Holding registers): Read CXC live signals from signals tables,
• 0x04 (Read Input registers): Read CXC relay or alarm table status registers.
Table S — Table N–CXC Modbus PDU address denition for function code 0x01 (read coils)
PDU Address Variable Name Variable Description Response Data Format
0x0001 Relay1_Status_Bit Relay 1 (K1) BINARY
0x0002 Relay2_Status_Bit Relay 2 (K2) BINARY
0x0003 Relay3_Status_Bit Relay 3 (K3) BINARY
0x0004 Relay4_Status_Bit Relay 4 (K4) BINARY
0x0005 Relay5_Status_Bit Relay 5 (K5) BINARY
0x0006 Relay6_Status_Bit Relay 6 (K6) BINARY
0x0007 Relay7_Status_Bit Relay 7 (K7) BINARY
0x0008 Relay8_Status_Bit Relay 8 (K8) BINARY
0x0009 Relay9_Status_Bit Relay 9 (K9) BINARY
0x000A Relay10_Status_Bit Relay 10 (K10) BINARY
0x000B Relay11_Status_Bit Relay 11 (K11) BINARY
0x000C Relay12_Status_Bit Relay 12 (K12) BINARY
0x000D Relay13_Status_Bit Relay 13 (K13) BINARY
0x000E Relay14_Status_Bit Relay 14 (K14) BINARY
0x000F Relay15_Status_Bit Relay 15 (K15) BINARY
0x0010 Relay16_Status_Bit Relay 16 (K16) BINARY