d0ff35b88d
Add DE/nRE gpios properties to samples and test. Signed-off-by: Johann Fischer <johann.fischer@nordicsemi.no>
128 lines
3.4 KiB
ReStructuredText
128 lines
3.4 KiB
ReStructuredText
.. _modbus-rtu-server-sample:
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Modbus RTU Server Sample
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########################
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Overview
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********
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This is a simple application demonstrating a Modbus RTU server implementation
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in Zephyr RTOS.
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Requirements
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************
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This sample has been tested with the nRF52840-DK and FRDM-K64F boards,
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but it should work with any board that has a free UART interface.
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Additionally the board should have three LEDs.
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RTU server example is running on an evaluation board. Client is running
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on a PC or laptop.
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In addition to the evaluation board, an USB to RS-485 bus adapter and
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a RS-485 shield are required. The shield converts UART TX, RX signals to RS-485.
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An Arduino header compatible shield like `joy-it RS-485 shield for Arduino`_
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can be used. This example uses DE signal, which is controlled by pin D9
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on the JOY-IT shield. For other shields, ``de-gpios`` property must be adapted
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or removed in the application overlay file
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:zephyr_file:`samples/subsys/modbus/rtu_server/app.overlay`
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The USB to RS-485 adapter connects to the USB port of a computer.
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The two A+, B- lines should be connected to the RS-485 shield.
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The description of this sample uses `PyModbus`_ (Pymodbus REPL).
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The user can of course try out other client implementations with this sample.
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Building and Running
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********************
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This sample can be found under
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:zephyr_file:`samples/subsys/modbus/rtu_server` in the Zephyr tree.
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The following commands build and flash RTU server sample.
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.. zephyr-app-commands::
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:zephyr-app: samples/subsys/modbus/rtu_server
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:board: nrf52840dk_nrf52840
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:goals: build flash
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:compact:
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On the client side, PC or laptop, the following command connects PyModbus
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to the RTU server.
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.. code-block:: console
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# pymodbus.console serial --port /dev/ttyUSB0 --baudrate 19200
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--bytesize 8 --parity N --stopbits 2
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The LEDs on the board are controlled by Modbus commands FC01, FC05, FC15.
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For example, to set LED0 on use FC01 command (write_coil).
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.. code-block:: console
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> client.write_coil address=0 value=1 unit=1
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Client should confirm successful communication and LED0 should light.
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.. code-block:: console
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{
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"address": 0,
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"value": true
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}
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To set LED0 off but LED1 and LED2 on use FC15 command (write_coils).
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.. code-block:: console
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> client.write_coils address=0 values=0,1,1 unit=1
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To read LED0, LED1, LED2 state FC05 command (read_coils) can be used.
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.. code-block:: console
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> client.read_coils address=0 count=3 unit=1
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{
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"bits": [
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false,
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true,
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true,
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false,
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false,
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false,
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false,
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false
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]
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}
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It is also possible to write and read the holding registers.
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This however does not involve any special interaction
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with the peripherals on the board yet.
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To write single holding registers use FC06 command (write_register),
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.. code-block:: console
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> client.write_register address=0 value=42 unit=1
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or FC16 command (write_registers).
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.. code-block:: console
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> client.write_registers address=0 values=42,42,42 unit=1
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To read holding registers use FC03 command (read_holding_registers).
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.. code-block:: console
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> client.read_holding_registers address=0 count=3 unit=1
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{
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"registers": [
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42,
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42,
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42
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]
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}
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.. _`joy-it RS-485 shield for Arduino`: https://joy-it.net/en/products/ARD-RS485
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.. _`PyModbus`: https://github.com/riptideio/pymodbus
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