FL4000
41
4.7 MODBUS Write Command Protocol (Query / Response)
A master device writes to a FL4000 register by sending a properly formatted 8-byte message
(Table 26).
Table 26: MODBUS Write Register Request
Byte
MODBUS
Range
Referenced to FL4000
1
st
Slave Address
1-247* (Decimal)
FL4000 ID (Address)
2
nd
Function Code
06
Preset Single Registers
3
rd
Register Address Hi
00
Not Used by FL4000
4
th
Register Address Lo
00-FF (Hex)
FL4000 Register Address Lo Byte
5
th
Preset Data Hi
00-03 (Hex)
FL4000 Hi Byte Command Data
6
th
Preset Data Lo
00-FF (Hex)
FL4000 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 FL4000 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 FL4000
1
st
Slave Address
1-247* (Decimal)
FL4000 ID (Address)
2
nd
Function Code
06
Preset Single Registers
3
rd
Register Address Hi
00
Not Used by FL4000
4
th
Register Address Lo
00-FF (Hex)
FL4000 Register Address Lo Byte
5
th
Preset Data Hi
00-FF (Hex)
FL4000 Hi Byte Command Data
6
th
Preset Data Lo
00-FF (Hex)
FL4000 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
FL4000. Upon receiving the query, the FL4000 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 FL4000 does not receive the query due to a communications error, then no
response is returned from the FL4000 and the master device will eventually process a
timeout condition for the query.
If the FL4000 receives the query, but detects a communication error (CRC, etc.), then
no response is returned from the FL4000 and the master device will eventually process
a timeout condition for the query.
If the FL4000 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