Manual
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Alpha Technologies Ltd. 034-136-C0 Rev B WC
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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.
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
Table N–CXC Modbus PDU address definition for function code 0x01 (read coils)
PDU Address Variable Name Variable Description Response Data Format
0x0001 Alarm1_In_Alarm_Table_1_Status_Bit Rectifier Fail BINARY
0x0002 Alarm2_In_Alarm_Table_1_Status_Bit Rectifier Minor BINARY
0x0003 Alarm3_In_Alarm_Table_1_Status_Bit Rect. Major Fail Count BINARY
0x0004 Alarm4_In_Alarm_Table_1_Status_Bit Rect. Minor Fail Count BINARY
0x0005 Alarm5_In_Alarm_Table_1_Status_Bit Rectifier Lockout BINARY
0x0006 Alarm6_In_Alarm_Table_1_Status_Bit Out Of Tolerance BINARY
0x0007 Alarm7_In_Alarm_Table_1_Status_Bit Rect. Comms Lost BINARY
0x0008 Alarm8_In_Alarm_Table_1_Status_Bit Rect. Equalize Activated BINARY
0x0009 Alarm9_In_Alarm_Table_1_Status_Bit Rect. AC Mains Fail BINARY
0x000A Alarm10_In_Alarm_Table_1_Status_Bit Max Rectifiers Exceeded BINARY
0x000B Alarm11_In_Alarm_Table_1_Status_Bit Fan Fail Alarm BINARY
0x000C Alarm12_In_Alarm_Table_1_Status_Bit Power Save BINARY
0x000D Alarm13_In_Alarm_Table_1_Status_Bit Urgent Rect. AC Mains Fail BINARY