© 2020 Van Putten Instruments BV | MAN-VP-LOGR-UK | Revision: 2001 | Date: 01-10-2020
9
Modbus settings
The following table holds the default communication parameters for modbus.
Parameter
Description
Modbus Address
1
Baudrate
38400 baud
Parity
No parity bit is used.
Stop-bits
1 stop bit is used.
Modbus registers
The following is an overview of the available modbus registers.
Name
Register
Description
Units
I 50Hz
1
Current at base frequency
0.1 AAC
I RMS
2
True RMS current
0.1 AAC
Frequency
3
Frequency
0.01 Hz
Protocol functions
For reading the 16 bit values, modbus supports the commands “Read Holding Registers” (0x03).
When addressing registers, the command contains the address minus 1, for instance registers 1..3
are addressed as 0..2.
The VPLog-i-R also supports the modbus scan protocol. This allows to change the modbus settings
and to request extra information from the module.
Modbus example
Example 1
The following example contains a request and response for 2 registers starting at register 2 (RMS
c frequency).
Request : 01 03 00 01 00 02 95 CB
Response: 01 03 04 13 88 13 88 73 CB
Data bytes
Description
Request
01
modbus address VPLog-i-R
03
Function
00 01
Starting register
00 02
Register count
95 CB
CRC
Response
01
VPLog-i-R modbus address
03
Function
04
Byte count
