Modbus Registers; Modbus Specifications; Mapping Documentation Of The Sicam Devices - Siemens SICAM Q200 7KG97 Manual

2.4

Modbus Registers

Modbus Specifications

2.4.1
NOTE
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The Modbus specification with a detailed explanation of the Modbus protocol is provided in:
•
Modbus over Serial Line
Specification & Implementation Guide
http://www.modbus.org
•
Modbus Application Protocol Specification
http://www.modbus.org
•
Modbus Messaging on TCP/IP Implementation Guide
http://www.modbus.org
Generally, we have to differentiate between the following elements in Modbus:
•
The register number
•
The register address in Modbus messages
Register Number
The register number characterizes a Modbus register using a 5-digit or 6-digit decimal number where the digit
with the highest value defines the register type:
•
0 – coil status register
•
1 – input status register
•
3 – input register
•
4 – holding register
Counting of the register number starts at 1 for each register type, for example, for the 5-digit display:
•
00127 = coil status register 127 (alternatively: coil 127)
•
400108 = holding register 108
Register Address
All address data in Modbus messages refer to the value 0. Therefore, register number and register address are
related as follows:
•
register address = register number - 1
The following applies to the above examples:
•
Coil 127 is addressed as 126 (007E
•
400108 is addressed as 107 (006B

Mapping Documentation of the SICAM Devices

2.4.2
The Modbus bus mapping documents for the individual SICAM devices use the register number to reference a
piece of information in the Modbus register set.
NOTE
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You find the Modbus bus mapping document (Excel table) for the SICAM Q200 devices under:
www.siemens.com/sicam-q200
SICAM, Multifunctional Recorder, Manual
E50417-C1040-C606-A3, Edition 03.2017
) in a Modbus message to query or describe the coil status register.
hex
) in a Modbus message to query or describe the holding register.
hex
Communication Modbus

2.4 Modbus Registers

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