© 2019 VPInstruments | MAN-VP-SPRO-EN | Revision: 1901 | Date: 04-07-2019
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9.3
Modbus interface
Introduction to Modbus
For a complete introduction on the Modbus standard can be found on www.modbus.org. See the
document Modbus_over_serial_line_V1_02.pdf, which can be downloaded from their website. We
strongly recommend to download and read this information carefully before installing Modbus
communication. The following paragraphs in this chapter assume you are familiar with the Modbus
communication standard.
All measurement parameters are available through Modbus in floating point and integer format. The
data will be refreshed every second. Maximum polling interval is 10ms.
Communication settings
The RS485 communication settings can be changed with VPStudio. Below shows the available
options
·
Baud rate: 9600 | 19200 | 38400
·
Stop bits: 1 | 2
·
Parity: None | Even | Odd
The Modbus settings can be changed with VPStudio, the hardware address can also be changed
with the keypad when available. Below shows all available options
·
Hardware address: 1-247
·
Integer multiplier: 1-1000
Data format
Function code 0x03 for reading(Holding register)
Function code 0x10 for writing (Holding register)
32-bit Floating point Little endian [CDAB]
32-bit signed Integer Little endian [CDAB]
Factory default settings
Parameters
Value
Baud rate
38400
Stop bits
1
Parity
None
Hardware address
9
Integer multiplier
10