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Overview
Modbus is a request/response protocol, where memory items are accessed by an identifier
number. Memory items come in four different types and are named for the legacy purpose of
controlling relay hardware.
▶ Coils are used to trigger actions on the Tracker, in this way they function as commands.
▶ Discrete inputs are used to read status and warning information.
▶ Input registers contain measure values.
▶ Holding registers contain configuration values which can be changed by the user
It should be noted that 16-bit registers can be signed or unsigned integers. Always refer to the
supporting documentation to verify if the data in a register should be treated as a signed or
unsigned quantity.
Larger values many need to be represented as long integers (32-bit). A special extension to the
Modbus specification is utilized to store these as two contiguous registers. As with 16-bit integers,
always check the supported documentation to understand if these quantities are signed or
unsigned. Values are stored with the least significant word in the lower addressed register.
The Tracker supports all Class 0 and Class 1 function codes except for Read Exception Status.
This code does not apply to the Tracker.
For more information about command formats, please review the following publicly-available
documents:
Modbus Application Protocol V1.1b3
Published by Modbus Organization, Inc.
http://www.modbus.org/docs/Modbus_Application_Protocol_V1_1b3.pdf
Modbus Protocol Reference Guide
Published by Modicon, Inc. (now Schneider Electric), Made Available by Modbus Organization, Inc.
http://modbus.org/docs/PI_MBUS_300.pdf
Type
Access
Data Type
Address Range
Coil
Read/Write
Boolean
00001-09999
Discrete Input
Read-Only
Boolean
10001-19999
Holding Register
Read/Write
16-bit
40001-49999
Input Register
Read-Only
16-bit
30001-39999
Summary of Contents for GAS TRACKER
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