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The Delta Controls fully programmable, Modbus gateway allows Delta products to map registers in Modbus slave devices into standard BACnet™ objects, which are then accessible on a BACnet™ network via available ports. Controllers become Masters to the connected Modbus slave devices and communicate using the Modbus RTU protocol on an RS-232 or RS-485 LAN, depending on controller hardware.

Application: The Delta Modbus products come in two categories, gateway and controller. Gateway products, pre-loaded with Modbus, provide a gateway to BACnet for multiple Modbus devices communicating on the same Modbus network (5, 15, or 30 Modbus slave devices).

Controller products with Modbus capability are used where a Delta I/O controller already exists, and there is a need to add Modbus devices as part of the same mechanical system. This provides support for communication of 1 to 5 Modbus slave devices using a standard controller by flash loading Modbus using an associated hardware key. Modbus capability via flash loading in the field is used for controllers using firmware V3.30R2 or higher, to a maximum 5 Modbus units.


  • Modbus protocol provides a common language for devices to exchange data between BACnet and Modbus
  • Supports Modbus capability via flash loading in the field
  • Supports flash loading Modbus upgrades via hardware key
  • Decimal scaling from 1/1000 to 1000 for imbedded integer to real number conversions
  • Assign bits within registers directly to Binary Variables
  • Display Exception Codes on a per register basis
  • Assign registers with 0 based (x0000) or 1-based (Register 1) offset to match documentation
  • Assign registers to multi-state variables directly with or without offset of 1 as required


Modbus RTU


RS-485, RS-232, UDP

Baud Rates

@ 9600, 19200, 38400 bps

Packet Structure

8 data bit, no parity, 1 stop bit (8-N-1)

Modbus Functions Supported

(01) Read Coil Status (0...)

(02) Read Input Status (1...)

(03) Read Holding Register (4...)

(04) Read Input Registers (3...)

(05) Force (Write) Single Coil (0)

(06) Preset (Write) Single Register (4....)

Built-in Gateway Features

Exception codes per entry

Decimal scaling (Value * .001 to 1000)

Bit extraction (Read Only)

Register Base Count offset (0 or 1)

Multistate offset (for MV translation)

Number of devices supported: up to 30 (device type dependent)

Note: For further information, review the DSM-RTR or DSM-T0B catalog sheets for respective hardware specifications.