Vaisala DPT146 Uživatelská příručka stáhnout pdf (Strana 53)

Chapter 5 _________________________________________________________________ Operation

VAISALA ________________________________________________________________________ 51

Modbus Communication

Addressing with Modbus Protocol

The Modbus variant used in DPT146 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 66.

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 DPT146

device, follow the procedure above and deactivate the Modbus mode

with command SMODE STOP. On subsequent power-ups, the serial

command interface will be activated.

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