Chapter 6 Communication Mode
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EH-SIO support function codes
The function code that EH-SIO supports shown in the following table.
Table 6.10 EH-SIO support functions
State of input status is read.
State of holding register is read.
State of input register is read.
State of coil changes between ON/OFF.
State of holding register is changed.
State of two or more coils changes between ON/OFF.
Preset Multiple Registers
State of two or more holding registers is changed
Exception code
When the contents of a query message are inaccurate or a slave cannot process the query, the slave returns an
exception response including error factor.
Table 6.11 Exception code list
Requested function is not supported
Specified data address does not exist in the slave.
Data value is not allowed for the slave.
An unrecoverable error occurred in the slave.
Although query is recognized, it takes time to reply. (To prevent timeout
error.)
Processing of previous query.
Reference : Modbus data address
Data address must be specified for data reading and writing. According to the “Modbus Protocol Reference Guide”
there are four types of data (coil, input status, input register, and holding register).
(1) Coil Bit data from 1 to 9,999 for reading and writing.
(2) Input status Bit data from 10,001 to 19,999 for reading only.
(3) Input register Word data from 30,001 to 39,999 for reading only.
(4) Holding register Word data from 40,001 to 49,999 for reading and writing.
Since data type is specified by function code, the address in message is only 4 digits. Moreover, if the address of a
message format is set to "0000", then the specified address is "x0001" (x being the maximum higher rank for each
data classification).
Ex.) Input register Data address 10789
4 low figures 789 Offset from Address 788 Specification of data address 0x0314
Hereafter, the explanation of each function code is written in accordance with this.
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