Sensia CamCor, Protocol Manual

Section 1—Modbus Protocol

This manual is for use with maintenance board firmware version 3.05.

Introduction

The communications protocol for CamCor CT Series and PRO Series is in accordance with Modicon, Inc. RTU Mode 

Modbus as described in 

Modicon Modbus Protocol Reference Guide

, PI-MBUS-300 Rev. J, June 1996. All registers are 

implemented as 4X or holding registers. Reading of registers is implemented via Function Code (03H) (Read Holding 

Registers). Writing to registers is implemented via Function Code 16 (10H) (Preset Multiple Registers). 

Communications

CamCor’s Modbus communications allow host devices (PC, sequencer, etc.) to connect to slave devices via RS-485 con

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nection. Modbus communication is based on the Master-Slave  system, where host devices are designated as “master” 

and the Coriolis meter(s) is designated as “slave.” The system is Modbus-protocol compliant. Contact the host device 

service provider for assistance with host software.

Caution 

If the CamCor meter is installed in a control system, place the control system in manual operating 

mode before making changes to the CamCor meter configuration. Failure to do so may cause er

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ratic and undesired responses from valves or other devices controlled by the system.

Consult 

Table 1.1—Communication Specifications

 below for CamCor Coriolis meter communication specifications.

Table 1.1—Communication Specifications

Specification

Description

Communication System

RS-485 Multidrop-compliant Master/Slave System

Full-duplex/Half-duplex

Half-duplex

Baud Rate

9600, 19200, 38400 (shipped from Factory at 9600)

Slave Address

1

Data Bits

8

Parity

Odd

Stop Bit

1 Bit

Flow Control

None

Communication Timeout

200 ms

Transmission Length (Maximum)

0.75 miles (1.2 km) (depending on service environment)

Number of Devices on Each Node 

(Maximum)

32 

Optional Modbus Communication Baud Rate Setting

A CamCor meter purchased with the Modbus Communication option is shipped with the baud rate set to 9600. The baud 

rate is adjustable using the SW3-1 and SW3-2 switches on the maintenance board (

Figure 1.1, Page 6

) located in the 

transmitter body. (For more information about maintenance board access and switch locations, see the CamCor Hardware 

Manual.) See 

Table 1.2—Baud Rate Switch Settings

 below to identify baud rate settings based on switch position:

Table 1.2—Baud Rate Switch Settings

Baud Rate

SW3-1 Setting

SW3-2 Setting

9600

Off

Off

19200

On

Off

38400

Off

On

5

CamCor

™

 Modbus Protocol 

 Section 1