42
Modbus Communication
8.4.2 Report Slave ID—Function Code 17 (11 Hex)
This command returns a description of the type of controller present at the
slave address.
8.4.3 Floating Point Support
The original Modbus protocol specification did not support floating point numbers.
These are implemented in the 9186 as IEEE 754 floating point numbers, and are
stored in two back-to-back 16 bit registers.
is an example that requests
the value from register 40001-40002.
Assume that the register combination 40001 and 40002 contains the 32-bit value
7.0 (see
).
Note that it is up to the master to decipher the floating point representation of the
4 bytes, based on the IEE 754 standard. If the floating point numbers are
displayed incorrectly, the word order may need to be swapped. See
for more information on swapping words within floating point numbers.
Data low byte
04
CRC high byte
2E
CRC low byte
B9
Table 18 Write Multiple Input Registers Response (continued)
Field Name
Hex Value
Table 19 Read Input Register Query
Field Name
Hex Value
Slave address
01
Function
03
Starting address high byte
00
Starting address low byte
00
Number of registers high byte
00
Number of registers low byte
02
CRC high byte
C4
CRC low byte
0B
Table 20 Read Input register Response
Field Name
Hex Value
Slave address
01
Function
03
Byte count
04
Data high byte (register 40001)
00
Data low byte (register 40001)
00
Data high byte (register 40002)
40
Data low byte (register 40002)
E0
CRC high byte
B9
CRC low byte
C9
