EPA SM-Ethernet, User Manual

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112
SM-Ethernet User Guide
Issue: 7
12.6 Supported Modbus function codes
Table 12.3 below, details the supported Modbus function codes on SM-Ethernet. All
function codes write to 16 bit registers only, to write to a 32 bit destination see section
12.6.1
Extended data types on page 112.
Table 12.3 Supported function codes
12.6.1 Extended data types
Standard Modbus registers are 16 bits in size and reference a single drive parameter
(Pr
xx.xx ). To support 32 bit data types (both integer and floating point) the Modbus
multiple read and write services are used to transfer a contiguous array of 16 bit
registers.
Control Techniques products typically contain a mix of 16 bit and 32 bit
registers. To permit the client to select the appropriate 16 bit or 32 bit access the top two
bits of the register address are used to select the required data type as shown in Figure
12-3.
Figure 12-3 Modbus register data type selection
The extended data types are defined such that the type ‘00’ allows for backwards
compatibility.
Table 12.4 Data type field
**Not currently supported.
Code Description
Decimal Hex.
3 0x03 Read multiple 16 bit registers.
6 0x06 Write single 16 bit register.
16 0x10 Write multiple 16 bit registers.
23 0x17 Read and write multiple 16 bit registers.
Control Techniques register numbers are referenced from 0 to 65535 rather than the
traditional 1 to 65536. This is because the Control Techniques implementation of
Modbus in the receiving node adds 1 to the register number effectively preventing
access to parameter Pr
00.00 within the drive.
NOTE
Type field
bits 15-14
Selected data type Comments
00 INT16 Backward compatible.
01 INT32 None.
10 Float 32**
IEEE794 standard not supported
on all servers.
11 Reserved None.
Control Techniques drive parameters currently do not support Float32 . To overcome
this INT32 should be used to represent 32 bit values. If a 32 bit data type is selected
then the server uses two consecutive 16 bit Modbus registers in 'big endian' format
(MSB transmitted first). For details of the data types within each product please consult
the documentation for that product or contact your supplier.
bit 15 bit 14 bit 13 - 0
Type
select
Parameter address
NOTE