Instruction manual

Startup

continued

RFT9739 Field-Mount Transmitter Instruction Manual

Output Wiring Startup TroubleshootingBefore You Begin Getting Started Mounting

Power-Supply and

Sensor Wiring

M3 — Data bits, protocol, and physical layer

The M3 screen enables selection of 7-bit or 8-bit mode for Modbus

protocol, or 8-bit mode for HART protocol.

• The HART protocol can use either the Bell 202 or RS-485 physical

layer.

• Using HART protocol over the primary mA output requires the Bell 202

physical layer.

To set the data bits and protocol:

1. Rotate and release the Scroll knob to view each data bits (D) option.

Choose from 7 data bits or 8 data bits. HART protocol requires 8 data

bits; Modbus protocol requires 7 data bits for ASCII mode or 8 data

bits for RTU mode.

2. Rotate and hold the Reset knob to select the displayed data bits.

Release the Reset knob when the display stops flashing.

3. When the selected data bits flashes again, rotate and release the

Reset knob to move to the protocol and physical layer options.

4. Rotate and release the Scroll knob to view each protocol/physical

layer option. Choose from the following:

• HART protocol over the Bell 202 physical layer (HART/202)

• HART protocol over the RS-485 physical layer (HART/485)

• Modbus protocol over the RS-485 physical layer (Modbus/485)

• Modbus protocol over the RS-485 physical layer and HART protocol

over the Bell 202 physical layer (Modbus/202)

5. Rotate and hold the Reset knob to select the displayed

protocol/physical layer. Release the Reset knob when the display

stops flashing.

6. When the selected protocol/physical layer flashes again, rotate and

release the Reset knob to restart the transmitter. If the

protocol/physical layer was not changed, the transmitter will not

restart, and display will return to the process variable screen.

CAUTION

Changing the protocol or data bits will cause the

process to shut down and the transmitter to initialize

as described on page 51, which could result in

switching of flow loop control devices.

Set control devices for manual operation before changing

the communications protocol.