GASSONIC OBSERVER-i
52
6.0
Modbus Digital Interface
The Gassonic Observer-i is available in a Dual Modbus configuration and in a Single HART
configuration. For the Dual Modbus configuration, two independent Modbus communication channels
are provided and referred to as Comm 1 and Comm 2. For the Single HART configuration,
the Modbus channel is referred to as Comm 1.
NOTE:
The Dual Modbus configuration disables HART communication.
6.1. Baud
Rate
The Baud Rate is a selectable setting via the Modbus communications interface. The selectable baud
rates are 57600, 38400, 19200, 9600, 4800, or 2400 bps.
6.2. Data
Format
The Data Format is a selectable setting via the Modbus communications interface. The selectable data
formats are as follows:
Data Bits
Parity
Stop Bit
Format
8 None 1 8-N-1
8
Even
1
8-E-1
8 Odd 1
8-O-1
8
None
2
8-N-2
Table 5: Data Format
6.3. Modbus
Read
Status
Protocol (Query/Response)
6.3.1. Modbus Read Query Message
Byte
Modbus
Range
Referenced to
Gassonic Observer-i
1
st
Slave
Address
1-247 *
Gassonic Observer-i ID (Address)
(X = 0 or 1 Model Type)
2
nd
Function
Code
03
Read Holding Registers
3
rd
Starting
Address Hi**
00
Not Used by Gassonic Observer-i
4
th
Starting
Address Lo**
00-FF (Hex)
Gassonic Observer-i Commands
5
th
No.
of
Registers Hi
00
Not Used by Gassonic Observer-i
6
th
No. of
Registers Lo
01
No. of 16 Bit Registers
7
th
CRC Lo
00-FF (Hex)
CRC Lo Byte
8
th
CRC Hi
00-FF (Hex)
CRC Hi Byte
Table 6: Modbus Query Messages
NOTE*:
Address 0 is reserved for broadcast mode and is not be supported at this time.
NOTE**:
Start Address can be a maximum of 247 Address Locations (0000-0x00F7).
