Commander SK Advanced User Guide
21
Issue Number: 9 www.controltechniques.com
The 2bit type field selects the data type according to the table below:
If a 32bit data type is selected then the slave uses two consecutive 16bit MODBUS registers (in 'big endian'). The master must also set the correct
'number of 16bit registers'.
Example, read Pr
20.21
through Pr
20.24
as 32bit parameters using FC03 from node 8:
Table 6-9 Master request
Table 6-10 Slave response
Reads when actual parameter type is different from selected
The slave will send the least significant word of a 32 bit parameter if that parameter is read as part of a 16 bit access.
The slave will sign extent the least significant word if a 16 bit parameter is accessed as a 32 bit parameter. The number of 16 bit registers must be
even during a 32 bit access.
Example, If Pr
20.21
is a 32 bit parameter with a value of 0x12345678, Pr
20.22
is a 16 bit parameter with a value of 0xABCD, and Pr
20.23
is a 16 bit
parameter with a value of 0x0123.
Type field
bits 15-14
Selected data
type
Comments
00
INT16 backward
compatible
01
INT32
10
Float32
IEEE754 standard
Not supported on all slaves
11
Reserved
Byte
Value
Description
0
0x08
Slave destination node address
1
0x03
FC03 multiple read
2
0x47
Start register address Pr
20.21
( 2021 - 1) = 18404 = 0x47E4
3
0xE4
4
0x00
Number of 16bit registers to read
Pr
20.21
through Pr
20.24
is 4x32bit registers =
8x16bit registers
5
0x08
6
CRC LSB
7
CRC
MSB
Byte
Value
Description
0
0x08
Slave destination node address
1
0x03
FC03 multiple read
2
0x10
Length of data (bytes) = 4x32bit registers =
16bytes
3-6
Pr
20.21
data
7-10
Pr
20.22
data
11-14
Pr
20.23
data
15-18
Pr
20.24
data
19
CRC LSB
20
CRC MSB
Summary of Contents for 2202
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