Circutor ReadWatt, Instruction Manual

Page: 14 / 24

4�3- COMMUNICATIONS
ReadWatt
has two communications ports, RS-232 and RS-485. Both ports can be used simultaneously.
The transmission speed, Baudrate, is the same for both ports and can be configured.
4�3�1�- MODBUS PROTOCOL
The MODBUS protocol is a communication standard in the industry that enables the network
connection of multiple devices, where there is a master and multiple slaves. Within the
MODBUS
protocol ReadWatt uses the RTU (Remote Terminal Unit) mode.
In RTU mode the start and end of the message is detected with silences with a minimum of 3.5
characters and the 16-bit CRC error detection method is used.
The MODBUS functions implemented in the device are:
Functions 03 and 04
. Reading of registers.
Function 10 . Writing of multiple registers.
4�3�2�- READ COMMANDS
ReadWatt
supports the integer type read functions:
0x03
and
0x04
.
The device's MODBUS variables are specified in
Table 6
.
Example: Reading of the device's serial number with peripheral number 01.
We will send the following MODBUS frame:
Address Function
Initial
Register
Register no� CRC
01 04 0060 0002 CRC
The device will respond to us with the next frame:
Address Function No� of bytes Serial no� CRC
01 04 04 XXXX XXXX CRC
Note: The values are shown in hexadecimal.
The number of requested logs must be the same as the size of the variable requested.
It is possible to read several consecutive addresses, if the request meets the correct format.
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ReadWatt
Instruction Manual