Communication
2.2 Modbus
22 SICAM Q100, 7KG95xx, System Manual
E50417-C1040-C522-A8, Edition 09.2020
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),
• 40108 = 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
hex
) in a Modbus message to query or describe the coil status register.
• 40108 is addressed as 107 (006B
hex
) in a Modbus message to query or describe the holding register.
2.2.5.2 Mapping Documentation of the SICAM Devices
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.
Only holding registers are used for SICAM Q100. All measured values, indications, metered values etc. are
stored in these holding registers.
Characterization of the register type (holding register) in the highest digit of the register number is not applica-
ble in the Modbus documentation of SICAM Q100.
2.2.6 Data Types
The following data types are used for storing variables in the Modbus registers.
• Measured value
• Date/time
• Indication
• Controllable indication
• Counter
•String
NOTE
The following convention applies when storing variables consisting of more complex data types to the Mod-
bus holding register (that is variables which are larger than a holding register, for example 32-bit measured
values):
The register with the lowest address contains the most significant byte (MSB), the register with the highest
address contains the least significant byte (LSB).
SYS_SICAM_Q100_US.book Page 22 Thursday, September 24, 2020 1:17 PM
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