Communication Guide, ©ComAp – March 2014 131
IGS-NT Communication Guide 03-2014.pdf
Examples of Modbus Communication
In this chapter are some examples, how does communicate controller via Modbus.
Battery voltage – reading (read multiple
registers)
Request: 01 03 00 0C 00 01 44 09
01 = Controller address
– see your controller settings
03 = Modbus function code (Read Multiple Registers)
00 0C = Register address: Register number (Ubat => 40013)
– 40013 - 40001 = 12 DEC => 000C HEX
– see your Cfg Image or list of dedicated communication objects
A part of Cfg Image (Modbus Register …)
00 01 = Number of registers
– 40013, it is one register = 01 DEC => 0001 HEX
– you have to calculate number of register which you want read
09 44 = CRC
–CRC has to be written LSB then MSB ! See how to calculate CRC. or
implementation in C language – page 118.
Response: 01 03 02 00 DC B9 DD
01 = Controller address
– see your controller settings
03 = Modbus function code (Read Multiple Registers)
02 = Length of read data in Bytes (in HEX)
– 02 HEX => 2 DEC
– define the length of data
00 DC = Value of battery voltage
– DC HEX => 220 DEC => Batt. voltage is represented with 1 decimal => 22,0
VDC
– convert the data from hex to dec. Use the multiplication factor (In this case
0.1) !
DD B9 = CRC
– check with your CRC, because of data validity
A part of Cfg Image (Modbus Register …)
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