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SM500F
Field mountable paperless recorder Appendix B – Modbus TCP/Modbus 485
Appendix B – Modbus TCP/Modbus 485
B.1 Introduction
The recorder can be configured to act as either a Modbus TCP client or server, or, when fitted with an optional Modbus/RS485 serial communications module, a Modbus RS485 (RTU) slave.
If configured as a client, the recorder collects data from Modbus TCP servers (or RTUs via a gateway) into its Comms Analog and Comms Digital Channels.
If configured as a server the recorder responds to Modbus queries transferred via the Modbus TCP or Modbus RS485 (RTU) protocol for the registers described in this appendix.
Note. The Modbus RS485 option provides the following facilities:
Standard RS422/485 communications.
Modbus RTU protocol – for master (host computer/plc) to slave.
500V DC isolation from external connections to the instrument.
Two-wire communication.
1200, 2400, 4800, 9600, 19200, 38400, or 115200 baud transmission rate. Parity-checking – odd, even or none.
B.2 Modbus Commands Supported
The following Modbus commands are supported:
01 ReadCoilStatus–readstheon/offstatusof16consecutivedigitalstates,startingataspecified address. The recorder returns zeros for points which do not contain defined data.
03 ReadHoldingRegisters–reads8consecutiveanalogvalues,startingfromaspecifiedaddress.The recorder returns zeros for registers which do not contain defined data.
05 ForceSingleCoil–Setsthevalueofasinglecoil(digitalsignal)atthespecifiedaddress.Thedata value must be FF00Hex to set the signal ON and zero to turn it OFF. The recorder returns an exception response if the register is not currently writable.
06 Preset Single Register – Sets the value of a single register (analog value) at the specified address. The recorder returns an exception response if the register is not currently writable. Limits defined in configuration are applied to the value before storage.
15 ForceMultipleCoils–Therecordercarriesoutupdatesthatarevalidandreturnsanexception response if any of the coils are not currently writable.
16 PresetMultipleRegisters–Therecordercarriesoutupdatesthatarevalidandgeneratesan exception response if any of the registers are not currently writable.
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