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Technical Notes
Features of the DeltaV Virtual IO Module Modbus TCP/IP Driver
By Martin Berutti
Product: IOD-4101 - Modbus TCP/IP Master Driver (General Modbus TCP/IP Communications)

This purpose of this technical note is to describe key features of the Virtual IO Module Modbus TCP/IP Driver.

To follow is a summary of the key features of the IOD-4101, Modbus TCP/IP Driver for the Virtual IO Module, that support greater connectivity to Modbus devices.

  1. Complete support of all capabilities of the standard DeltaV Modbus Driver.
  2. Absolute table indexing - any address space can be accessed from register start address to offset of 65535. eg.: if holding registers start at 400,000, registers up to 465,535 can accessed.
  3. User configurable Floating Point Byte order. User can characterize floating point byte order for most significant, least significant byte.
  4. Supports all 3 variants of the Modbus TCP/IP protocol on the same VIM and to the same device (if required) including:
  • RTU TCP - Open Modbus messaging using TCP/IP
  • RTU via TCP - Modbus encapsulated in TCP/IP messages
  • RTU via UDP - Modbus encapsulated in UDP broadcast messages
  1. Support for multiple masters, multiple slaves
  • Modbus Master mode only - 32 slaves supported per master
  • Modbus Master and Slave mode - 16 slaves per master, 16 masters per slave
  • Redundant Master mode - 16 slaves supported by master
  1. Seamless support of Modbus Gateways including Ethernet to Serial and Ethernet to ModbusPlus. Up to 16 Modbus addresses can be associated with a single TCP/IP address.
  1. Performance enhancement for better process controls and speed of response.
  • Devices can be configured to allow communications for up to 16 simultaneous messages in Master or Slave mode.
  • Output datasets can be configured to write all outputs upon a periodic cycle as well as upon change of state.
  • Each dataset can be set for an scan time offset to reduce data requests to heavily loaded slave devices.