41
Model FL4000H
4.7 Modbus Write Command Protocol (Query / Response)
A master device writes to a FL4000H register by sending a properly formatted 8-byte message
(Table 26).
Table 26: Modbus Write Register Request
Byte Modbus Range Referenced to FL4000H
1
st
Slave Address 1-247* (Decimal) FL4000H ID (Address)
2
nd
Function Code 06 Preset Single Registers
3
rd
Register Address Hi 00 Not Used by FL4000H
4
th
Register Address Lo 00-FF (Hex) FL4000H Register Address Lo Byte
5
th
Preset Data Hi 00-03 (Hex) FL4000H Hi Byte Command Data
6
th
Preset Data Lo 00-FF (Hex) FL4000H Lo Byte Command Data
7
th
CRC Hi 00-FF (Hex) CRC Hi Byte
8
th
CRC Lo 00-FF (Hex) CRC Lo Byte
* Address 0 is reserved for Broadcast Mode and is not supported at this time.
Upon receiving a valid register write request from the master device, the FL4000H will respond
with a message (Table 27). If the write request generates an error, an exception message is
returned to the master device (Section 4.8 ).
Table 27: Modbus Write Register Response
Byte Modbus Range Referenced to FL4000H
1
st
Slave Address 1-247* (Decimal) FL4000H ID (Address)
2
nd
Function Code 06 Preset Single Registers
3
rd
Register Address Hi 00 Not Used by FL4000H
4
th
Register Address Lo 00-FF (Hex) FL4000H Register Address Lo Byte
5
th
Preset Data Hi 00-FF (Hex) FL4000H Hi Byte Command Data
6
th
Preset Data Lo 00-FF (Hex) FL4000H Lo Byte Command Data
7
th
CRC Hi 00-FF (Hex) CRC Hi Byte
8
th
CRC Lo 00-FF (Hex) CRC Lo Byte
* Address 0 is reserved for Broadcast Mode and is not supported at this time.
4.8 Exception Responses and Exception Codes
4.8.1 Exception Response
In a normal communications query and response, the master device sends a query to the
FL4000H. Upon receiving the query, the FL4000H processes the request and returns a
response to the master device. An abnormal communication between the two devices produces
one of four possible events:
If the FL4000H does not receive the query due to a communications error, then no
response is returned from the FL4000H and the master device will eventually process a
timeout condition for the query.
If the FL4000H receives the query, but detects a communication error (CRC, etc.), then
no response is returned from the FL4000H and the master device will eventually
process a timeout condition for the query.
If the FL4000H receives the query without a communications error, but cannot process
the response within the master’s timeout setting, then no response is returned from the
FL4000H. The master device eventually processes a timeout condition for the query in
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