Rockwell Automation 900 Temperature Controller Communications Functions - Series B - Manual (Page 68)

Publication 900-UM004D-EN-E - July 2010
4-10 Modbus Communications Procedure
Figure 4.8 Response Frame
Table 4.7
Name Description
Slave address The value from the command frame is entered as-is.
Function code This is the received function code.
When the function ended normally, the function code is left as-is.
When an error occurred, the hexadecimal value of H’80 is added to
the function code to indicate that the response is an error response.
Example: Received function code = H’03
Function code in response frame when an error occurred = H’83
Byte count Contains the number of bytes of read data.
Number of
elements Contains the number of setting data items that were read.
CRC-16 This check code is calculated with the data from the slave address
to the end of the data.
For details on the CRC-16 calculation, refer to CRC-16 Calculation
Example on Page 4-2.
Table 4.8 Response Code
Function
Code Error
Code Error Name Cause
H’83 H’02 Variable address error The read start variable address is
incorrect.
The variable area number is incorrect.
H’03 Variable data error The number of elements exceeds the
allowed range.
H’03 — Normal completion No errors were found.
Slave
address
Function
code
Byte
count
1 1 1 2
CRC-16
0 to 212 (2
×
106)
Read data (for the
number of elements)
H'03