Model S4000TH
37
If the S4000TH 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 S4000TH. The master device eventually processes a timeout
condition for the query. In order to prevent this condition from occurring, the maximum
response time for the S4000TH is 200 milliseconds. Therefore, the master’s timeout
setting should be set to 200 milliseconds or greater.
If the S4000TH receives the query without a communications error, but cannot process
it due to reading or writing to a non-existent S4000TH command register, then the
S4000TH returns an exception response message informing the master of the error.
The exception response message (ref. No. 4 above) has two fields that differentiate it from a
normal response:
Byte
Modbus
Range
Referenced to S4000TH
1
st
Slave Address
1-247* (Decimal)
S4000TH 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
8.6.2 Exception
Code
Exception Code Field:
In a normal response, the S4000TH returns data and status in the data
field, which was requested in the query from the master. In an exception response, the
S4000TH returns an exception code in the data field, which describes the S4000TH condition
that caused the exception. Below is a list of exception codes that are supported by the
S4000TH:
Code
Name
Description
01 Illegal
Function
The function code received in the query is not an
allowable action for the S4000TH
02
Illegal Data Address
The data address received in the query is not an
allowable address for the S4000TH.
03
Illegal Data Value
A value contained in the query data field is not an
allowable value for the S4000TH.
04
Slave Device Failure
An unrecoverable error occurred while the S4000TH
was attempting to perform the requested action.
05 Acknowledge
The S4000TH 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 S4000TH 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
