4
Data are the data required for executing function codes. The composition of data varies
with function codes. Refer to chapter 6 for details.
A data address is assigned to each data in the temperature controller. For reading/writing the data
by communication, designate the data address.
5. CRC check
This is the code to detect message errors (change in bit) in the signal transmission.
On the MODBUS protocol (RTU mode), CRC-16 (Cyclical Redundancy Check) is applied.
For CRC calculation method, refer to section 5.5.
6. End
Following the last transmitted character, a similar interval of at least 3.5 character times
marks the end of message. A new message can begin after this interval.
5.3 Response of Slave Station
1. Response for normal command
To a relevant message, the slave station creates and sends back a response
message, which corresponds to the command message. The composition of
message in this case is the same as in section 5.2. Content of the data field
depend on the function code. For details, refer to Chapter 6.
2. Response for abnormal command
If contents of a command message have an abnormality (for example,
non-actual function code is designated) other than transmission error, the slave
station does not execute that command but creates and sends back a response
message at error detection.
The composition of response message at error detection is shown on below, the
value used for function field is function code of command message plus 80H.
ADDRESS FUNCTION (Function code + 80H)
ERROR CODE
CRC CHECK
8 BITS
8 BITS
8 BITS
16 BITS
Error Code
Contents
Description
01 Illegal
function
The
function
code received is not an allowable
action for the slave.
02
Illegal data address
The data address received is not an allowable
address for the slave.
03
Illegal data value
A value contained in the data field is not
an allowable value for the slave.
5.4 Function Code
The listing below shows the function codes supported by SE series controllers.
Function code
Code Function
Object
03 Read-out
Holding
Register
04 Read-out
Input Register
06
Write-in
Holding Register
5.5 Calculation of Error Check Code (CRC-16)
CRC-16 is the 2-bytes (16-bits) error check code. From the top of the message (address) to
the end of the data field are calculated.
The slave station calculates the CRC of the received message, and does not respond if the
calculated CRC is different from the contents of the received CRC code.
A procedure for generating a CRC is:
1. Load a 16-bits register with FFFF hex (all 1’s). Call this the CRC register.
2. Exclusive OR the first 8-bit byte of the message with the low-order byte of the 16-bit
CRC registers, putting the result in the CRC register.
