User`s guide

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
Reference on page 60.
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.