S4000C
28
3. If the S4000C receives the query without a communications error, but cannot process
the response to the master within the master’s timeout setting, then no response is
returned from the S4000C. The master device will eventually process a timeout
condition for the query.
In order to prevent this condition from occurring, the
maximum response time for the S4000C is 200 milliseconds. Therefore the
master’s timeout setting should be set to 200 milliseconds or greater.
4. If the S4000C receives the query without a communications error, but cannot process it
due to reading or writing to a non-existent S4000C command register, then the S4000C
will return an exception response message informing the master of the error.
Byte
MODBUS
Range
Referenced to S4000C
1
st
Slave Address
1-247* (Decimal)
S4000C ID (Address)
2
nd
Function Code
83 or 86 (Hex)
MSB is set with Function Code
3
rd
Exception Code
01 - 06 (Hex)
Appropriate Exception Code (See
Below)
4
th
CRC Lo
00-FF (Hex)
CRC Lo Byte
5
th
CRC Hi
00-FF (Hex)
CRC Hi Byte
The exception response message (ref. No. 4 above) has two fields that differentiate it from a
normal response:
8.6.2 Exception
Code
Exception Code Field:
In a normal response, the S4000C returns data and status in the data
field, which was requested in the query from the master. In an exception response, the S4000C
returns an exception code in the data field, which describes the S4000C condition that caused
the exception. Below is a list of exception codes that are supported by the S4000C:
Code
Name
Description
01
Illegal Function
The function code received in the query is not an
allowable action for the S4000C.
02
Illegal Data Address
The data address received in the query is not an
allowable address for the S4000C.
03
Illegal Data Value
A value contained in the query data field is not an
allowable value for the S4000C.
04
Slave Device Failure
An unrecoverable error occurred while the
S4000C was attempting to perform the requested
action.
05
Acknowledge
The S4000C has accepted the request and is
processing it, but a long duration of time will be
required to do so. This response is returned to
prevent a timeout error from occurring in the
master.
06
Device Busy
The S4000C is engaged in processing a long-
duration program command. The master should
retransmit the message later when the slave is
free.
Table 10: Exception Codes