Modbus Protocol for ION 7500, ION 7600 and ION 8000 series

Invalid Registers Modbus Register MapPreset Multiple RegistersPreset Registers Request Packet(Master station to meter)Preset Registers Response Packet(meter to Master station)Unit ID/Slave Address (1 byte)Unit ID/Slave Address (1 byte)16 (Function code) (1byte) 16 (Function code) (1 byte)Start Register (sr) (2 bytes)Start Register (sr) (2 bytes)# of Registers to Write (nr) (2 bytes) # of Registers Written (nr) (2 bytes)Byte Count (2 x nr) (1 byte)CRC Checksum (2 bytes)First Register in range (2 bytes)Second Register in range (2 bytes)...CRC Checksum (2 bytes)NOTEExcept for the function field,the Preset Registers Responsepacket is identical in format tothe Read Registers Requestpacket.Example:A meter is configured as a Modbus slave device with slave address 200. The Masterstation requests to set the PT ratio to 1200:120. From the register map, the PowerMeter PT Primary and Secondary setup registers are Modbus registers 46001/2 and46003/4. Register 46001 is numbered 6000. The request must write 4 registersstarting at 6000.Slave address: 200 = C8(hex) Start register 6000 = 1770 (hex)Value 1: 1200 = = 0000 | 04B0 (hex) Value 2: 120 = 0000 | 0078 (hex)Request Packtet: white background denotes the DATA field of the packet.SlaveFunctionStartRegister(46001)# ofRegisters(4)ByteCountRegister 1 Register 2 Register 3 Register 4 CRC ChecksumC8* 10 17 70 00 04 08 00 00 04 B0 00 00 00 78 8B F8Response Packet:Slave Function Start Register (46001) # of Registers (4) CRC ChecksumC8 10 17 70 00 04 D4 3C*The values shown in illustrated packets are represented in hexadecimal format.Invalid RegistersIn the meter Modbus register map, there are gaps between some registers. Forexample, the next register after 42232 is 42301. Unmapped registers (42233 throughto 42300) are INVALID. Invalid registers store no information.When an invalid register is read, the data field is FFFF(hex). When an invalidregister is written, the data field is not stored. The meter does not reject the request.Page 10