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Model S4000TH
8.4 Modbus Write Command Protocol (Query/Response)
8.4.1 Modbus Write Query Message
Byte
Modbus
Range
Referenced to S4000TH
1
st
Slave Address
1-247* (Decimal)
S4000TH ID (Address)
2
nd
Function Code
06
Preset Single Register
3
rd
Register Address Hi
00
Not Used by S4000TH
4
th
Register Address Lo
00-FF (Hex)
S4000TH Commands
5
th
Preset Data Hi
00-FF (Hex)
S4000TH Hi Byte Command Data
6
th
Preset Data Lo
00-FF (Hex)
S4000TH Lo Byte Command Data
7
th
CRC Lo
00-FF (Hex)
CRC Lo Byte
8
th
CRC Hi
00-FF (Hex)
CRC Hi Byte
*NOTE:
Address 0 is reserved for broadcast mode and will not be supported at this time.
**NOTE:
Start Address can be a maximum of 9999 Address Locations (0000-270E).
8.4.2 Modbus Write Response Message
Byte
Modbus
Range
Referenced to S4000TH
1
st
Slave Address
1-247* (Decimal)
S4000TH ID (Address)
2
nd
Function Code
06
Preset Single Register
3
rd
Register Address Hi
00
Not Used by S4000TH
4
th
Register Address Lo
00-FF (Hex)
S4000TH Commands
5
th
Preset Data Hi
00-FF (Hex)
S4000TH Hi Byte Command Data
6
th
Preset Data Lo
00-FF (Hex)
S4000TH Lo Byte Command Data
7
th
CRC Lo
00-FF (Hex)
CRC Lo Byte
8
th
CRC Hi
00-FF (Hex)
CRC Hi Byte
8.5 Function Codes Supported
Function Code 03 (Read Holding Registers) is used to read status from the slave unit.
Function Code 06 (Preset Single Register) is used to write a command to the slave unit.
8.6 Exception Responses and Exception Codes
8.6.1 Exception
Response
In a normal communications query and response, the master device sends a query to the
S4000TH and the S4000TH receives the query without a communications error and handles
the query normally within the master device’s allowable timeout. The S4000TH then returns a
normal response to the master. An abnormal communications produces one of four possible
events:
If the S4000TH does not receive the query due to a communications error, then no
response is returned from the S4000TH and the master device eventually processes a
timeout condition for the query.
If the S4000TH receives the query, but detects a communication error (CRC, etc.), then
no response is returned from the S4000TH and the master device eventually
processes a timeout condition for the query.