Monitor - Reading The Displayed Value Using Modbus Rtu Over Rs232 - Michell Instruments Easidew Online User Manual

Easidew Online User's Manual
3.6 Monitor – Reading the Displayed Value Using Modbus RTU Over RS232
It is possible to communicate with the online monitor using Modbus RTU over RS232.
The monitor has a three pin serial port connection on the back – the required cable can
be supplied by Michell (see Appendix B for set-up information).
To read the value displayed on the monitor a byte array must be created, containing
the following bytes:
Instrument
Address
0x01
Send this to the instrument with the correct delays between characters:
Baud Rate (bps)
1200
2400
4800
9600
19200
After a few seconds the instrument will send back the following response:
Instrument
Address
0x01
Data MSB * 256 + Data LSB = 0 *256 + 103 = 103
This code, written in c, can be used to convert the 103 into a real dew-point value or
10.3:
fl oat ConvertToReal(int Value) //convert dew-point value to real dew-point result
if (Value > 32767) Value=(Value-65536); //convert to negative number
result = (fl oat)(Value/10.0); //divide number by 10 to convert to fl oat
Michell Instruments
Reg
Command Address
High
0x04 0x00
Min Delay (ms)
Number of
Command
bytes
0x03 0x02
{fl oat result; //declaration
return result; //return real value}
Reg Number
Address of Reg
Low High
0x00 0x00
9.17
4.59
2.30
1.15
0.57
Display Display
High Low
0x00 0x67
OPERATION
Number
of Reg LRC CRC
Low
0x01 0x31 0xCA
Max Delay (ms)
13.76
6.88
3.44
1.72
0.86
LRC CRC
(Varies) (Varies)
39