Modbus communication, Addressing with modbus protocol, Accessing serial port command interface from – Vaisala DPT145 User Manual
Page 45: Modbus mode
Chapter 5 _________________________________________________________________ Operation
VAISALA ________________________________________________________________________ 45
Modbus Communication
Addressing with Modbus Protocol
The Modbus variant used in DPT145 communication is Modbus RTU.
An example of Modbus addressing is shown below.
Request:
0x01 0x03 0x00 0x04 0x00 0x02 0x85 0xCA
addr. func.
reg. 5
2 registers CRC check
Response: 0x01 0x03 0x04 0xBC 0xC0 0x41 0xC2 0x6E 0x5E
addr. func. len.
reg. 5
reg. 6
CRC check
For a list of available Modbus registers, see Appendix A, Modbus
Accessing Serial Port Command Interface from
Modbus Mode
You cannot change configuration settings (other than Modbus address)
while the device is in the Modbus mode. To use the configuration
commands on a Modbus-enabled device:
1.
Connect the USB service cable to the PC and install the driver, if
necessary.
2.
Open the terminal program and open a connection to the
corresponding COM port using settings 19200, 8, N, 1, no flow
control.
3.
Plug the service cable to the connector II of the instrument.
4.
In less than five seconds, send a hash character (
#
) and carriage
return (Enter) to the device using the terminal program. The device
is now ready for configuration commands. The Modbus mode is
restored on next power-up unless Modbus is disabled with
command
SMODE
.
For example, if you want to deactivate the Modbus mode on a DPT145
device, follow the procedure above and deactivate the Modbus mode
with the command SMODE STOP. On subsequent power-ups, the serial
command interface will be activated.