General Monitors FL4000H, Quick Start Manual

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40
Model FL4000H
4.5 Supported Function Codes
The FL4000H supports the following function codes:

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.
4.6 Modbus Read Status Protocol (Query / Response)
A master device reads registers from the FL4000H by sending an 8-byte message (Table 24).
Table 24: Modbus Read Register(s) Request
Byte Modbus Range Referenced to FL4000H
1
st Slave Address 1-247
*
(Decimal) FL4000H ID (Address)
2
nd Function Code 03 Read Holding Registers
3
rd
Starting Address Hi 00 Not Used by the FL4000H
4
th
Starting Address Lo 00-44 (Hex) FL4000H Commands
5
th
Number of Registers Hi 00 Not Used by the FL4000H
6
th
Number of Registers Lo
**
01 – 45 (Hex) Number of 16 Bit Registers
7
th
CRC Lo 00-FF (Hex) CRC Lo Byte
8
th
CRC Hi 00-FF (Hex) CRC Hi Byte
*
Address 0 is reserved for Broadcast Mode and is not supported at this time.
**
A maximum of 69 registers can be requested during a single block of time.
Upon receiving a valid read register request from the master device, the FL4000H will respond
with a message (Table 25). If the query generates an error, an exception message is returned
to the master device (Section 4.8 ).
Table 25: Modbus Read Register(s) Response
Byte Modbus Range Referenced to FL4000H
1
st
Slave Address 1-247* (Decimal) FL4000H ID (Address)
2
nd Function Code 03 Read Holding Registers
3
rd Byte Count ** 02 – 8A (Hex) Number of Data Bytes (N
+
)
4
th
Data Hi ** 00-FF (Hex) FL4000H Hi Byte Status Data
5
th
Data Lo ** 00-FF (Hex) FL4000H Lo Byte Status Data
:
:
:
: :
: :
:
N
+
+4
CRC Hi 00-FF (Hex) CRC Hi Byte
N
+
+5
CRC Lo 00-FF (Hex) CRC Lo Byte
*
Address 0 is reserved for Broadcast Mode and is not supported at this time.
**
Byte count and the number of returned data bytes depends on the number of requested
registers.
+ N denotes the number of returned data bytes.