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875 Benzene Monitor Manual
RS485 Modbus Interface
The Titan Modbus interface uses Serial ASCII format Modbus, at:
38400 baud 8 data bits, no parity, 2 stop bits.
Function Codes
Titan supports these function codes:
0x03 – Read Holding Registers
0x04 – Read Input Registers
0x10 – Write Multiple Registers
The address map for Read Holding Registers and Write Multiple Registers is the same – but not all addresses
are writeable.
Bytes and Words
Modbus registers are generally 16 bits in length. For example if you send the command to Read Input Registers
with a register quantity of 1 you will receive 2 bytes (1 word) of data. In the tables of addresses, we specify the
length in bytes. This is the number of bytes of data associated with the read/write at that address.
Thus your Modbus request will be for half that number of registers.
Input Registers Address Map
Use the function code 0x04 to Read Input Registers in the address range given in the table. If you read more
than the number of bytes indicated for the length at each address, any bytes beyond the length are undefined.
For example, if you read 32 bytes at address 1000, only the first 16 bytes returned are valid.
Address
Data
Content
(hex)
Length
(bytes)
0
60
Returns block of 15 integers for latest result
Integer Meaning
80
24
Returns block of data indicating the state of the
sensor temperature controller. Six 32-bit integers are
returned. e.g.
00000000 84 13 00 00 22 02 00 00 AD 08 00 00 A0 0F 00 00
„···"······ ···
00000010 01 00 00 00 01 00 00 00
These can be decoded as follows:
84 12 00 00 = 0x00001284 = 4740
The values have the following meaning
Integer
1
2
3
1
Benzene value in ppm x 10
2
Sensor temperature in degC x 100
3
Ambient temperature in degC x 10
4
Flow in ml/min x 100
5
PS1 diagnostic
6
PS2 diagnostic
7
PS3 diagnostic
8
Slope diagnostic
9
Flags
10
Sensor fence signal
11
Raw signal
12
STEL value
13
Pump drive signal
14
Pump drive volts
15
Fault record
Meaning
Temperature in degrees Celsius x 100
Ambient temperature in degC x 16
Heater drive power in % x 100
Page 18 of 65
Ion Science Ltd.
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