Chapter 8 Modbus Communication
8-7
•
S3 format is as below.
Bit15 Bit 8 Bit1 Bit0
•
NDR : when the communication ends normally, this bit turns on during 1 scan.
•
Error bit: when communication error occurs, this bit turns on during 1 scan. At that time, error code
stores bit 8 ~ bit 15.
•
Error code : Displays the Error information. Refer to detailed description as below table.
Error Code Table
Code
Error type
Meaning
01
Illegal Function
Error in inputting function code in instruction.
02 Illegal
Address
Error of exceeding the area limit of reading/writing on the slave
station.
03
Illegal Data Value
Error when the data value to be read from or write on the slave
station isn’t allowed.
04
Slave Device Failure
Error status of the slave station.
05 Acknowledge
It’s a responding code of the slave station for the master station to
prevent the master station time-out error, when request command
processing takes time. The master station marks an error code and
waits for a certain time without making any second request.
06
Slave Device Busy
Error when request command processing takes too much time. The
master should request again.
07 Time
Out
Error when exceeds the time limit of the communication parameter
as it communicates.
08
Number Error
Errors when data is 0 or more than 256 bytes
09
Parameter Error
Error of setting parameters (mode, master/ slave)
10 Station
Error
Error when the station number of itself and the station number
set by the S1 of instruction are the same.
Error Code (Bit8 ~Bit15)
Error Bit
(Bit1)
NDR(Bit)
