Appendix B - Modbus Tcp/Modbus 485; Introduction; Modbus Commands Supported - ABB SM500F User Manual

SM500F
Field mountable paperless recorder
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 Read Coil Status – reads the on/off status of 16 consecutive digital states, starting at a specified
address. The recorder returns zeros for points which do not contain defined data.
03 Read Holding Registers – reads 8 consecutive analog values, starting from a specified address. The
recorder returns zeros for registers which do not contain defined data.
05 Force Single Coil – Sets the value of a single coil (digital signal) at the specified address. The data
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 Force Multiple Coils – The recorder carries out updates that are valid and returns an exception
response if any of the coils are not currently writable.
16 Preset Multiple Registers – The recorder carries out updates that are valid and generates an
exception response if any of the registers are not currently writable.
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Appendix B – Modbus TCP/Modbus 485
IM/SM500F Rev. Z