STATUS SCIENTIFIC CONTROLS
Installation, Commissioning & Routine Gas Testing
FGD10A-M Gas Detector
TD18/032
Issue:
10
Change Note:
1869
Page 77
An identical method was used to generate the CRC for transmitted
messages.
10.3.3. Example 3: Received Modbus frame from FGD10AM
An typical response packet received from the FGD10AM to the command
sent in Example 1 would be:
Slave
address
Function
command
Byte
Count
Byte1
Byte 2
CRC checksum
0x01
0x03
0x02
0x00
0x32
0x39
0x91
i.e. a Gas reading of 0x0032=50% LEL from FGD10AM at network address
1.
10.3.4. Example 4: Write Calibration gas level to Modbus
register 40126
Mitsubishi FX3U PLC ladder diagram:
Flag M98 is set to trigger the write process which is then reset automatically
by M8029
Once the write command is completed D300 controls the ladder sequence.
H1 is the Modbus device node address.
H6 is the write single register command.
D302 contains the logical address of the Modbus register to be written to.
K0 is “don't care”
K50 “change the calibration gas level to 50%”
1
M98
125
─[= D300 K1 ]──| |──[ADPRW H1 H6 D302 K0 K50]───
M8029
──| |────────────[RST M98]─
In terms of a conventional Modbus packet sent to the FGD10AM this would
look like:
Slave
address
Function
command
Target
Register
Data to be written
CRC checksum
0x01
0x06
0x00 0x7D
0x00
0x32
0x98
0x07
