SI-Ethernet User Guide 121
Issue: 1
Safety
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Introduction
Mechanical
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Electrical
installation
Getting started Parameters
Key features
and Protocols
PC Applications Security Diagnostics
Glossary of
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7.2.3 Data access
Data access using Modbus TCP/IP takes the form of a request for data by the master,
followed by a response from the slave indicating success or failure. If no response is
received this indicates that the message has not been received or the message is
invalid or the node is unable to reply.
Each drive or option module parameter is internally mapped to a single 16-bit Modbus
register, all Modbus function codes access 16-bit registers only. To access a 32-bit
parameter, two contiguous Modbus registers must be specified in the request and the
32-bit data access scheme must be used.
7.2.4 32-bit data access
Standard Modbus registers are 16 bits in size and reference a single drive/option
module parameter. To access a 32-bit data value the multiple read/write services must
be used to transfer a contiguous array of 16-bit registers. To instruct the client to select
either 16-bit or 32-bit access bit 14 of the register address is used.
Figure 7-2 Data type selection
If 32-bit data type is selected then this effectively adds 16384 (0x4000) to the start
register address.
e.g. For drive parameter Pr 01.021 in standard addressing mode, the start register
value is 16384 + 120 = 16504 (0x4078)
7.2.5 Supported Modbus function codes
The following table details the supported Modbus function codes.
Table 7.4 Supported Modbus function codes
Bit b15 of the register address is reserved for future use.
Function Code
Description
Decimal Hex (0x)
303
Read multiple 16-bit registers
606
Write single 16-bit register
16 10
Write multiple 16-bit registers
23 17
Read and write multiple 16-bit registers
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