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User Guide: LDRA6 Appendix A: Modbus Communications
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A-2 PACKET COMMUNICATIONS FOR THE LDRA6
A-2.1 Read Output Registers
To read the LDRA6 parameter values, the master must send a Read Output Registers request packet. The
Read Output Registers request packet specifies a start register and the number of registers to read. The start
register is numbered from zero (40001 = zero, 40002 = one, etc).
Table 1: Read Output Registers Packet Structure
Read Registers Request Packet Read Registers Response Packet
Slave Address (1 byte) Slave Address (1 byte)
03 (Function code) (1 byte) 03 (function code) (1 byte)
Start Register (2 bytes) Byte count (1 byte)
# of registers to read (2 bytes) First register (2 bytes)
Crc Checksum (2 bytes) Second register (2 bytes)
…
Crc Checksum (2 bytes)
Table 2: Output Registers
Register Name Description Units Range
40001 Leak Threshold Zone 1 Trip current for leak alarm uAmps 0-65535
40002 Leak Threshold Zone 2 Trip current for leak alarm uAmps 0-65535
40003 Leak Threshold Zone 3 Trip current for leak alarm uAmps 0-65535
40004 Leak Threshold Zone 4 Trip current for leak alarm uAmps 0-65535
40005 Leak Threshold Zone 5 Trip current for leak alarm uAmps 0-65535
40006 Leak Threshold Zone 6 Trip current for leak alarm uAmps 0-65535
40007 Reserved
40008 Reserved
40009 Reserved
40010 Silence Alarm Set to 1 to silence audible alarm 1 = Silence 0-65535
40011 Reset Alarm Set to 1 to reset alarms 1 = Reset Alarm 0-65535
40012 Reserved
40013 Reserved
40014 Reserved
40015 Reserved
40016 Reserved
40017 Reserved