.. zephyr:code-sample:: modbus-rtu-client :name: Modbus RTU client :relevant-api: modbus Communicate with a Modbus RTU server. Overview ******** This is a simple application demonstrating a Modbus RTU client implementation in Zephyr RTOS. Requirements ************ This sample has been tested with the nRF52840-DK and FRDM-K64F boards, but it should work with any board that has a free UART interface. RTU client example is running on an evaluation board and communicates with another board running the :zephyr:code-sample:`modbus-rtu-server` sample. In addition to the evaluation board a RS-485 shield may be used. The shield converts UART TX, RX signals to RS-485. An Arduino header compatible shield like `joy-it RS-485 shield for Arduino`_ can be used. This example uses DE signal, which is controlled by pin D9 on the JOY-IT shield. For other shields, ``de-gpios`` property must be adapted or removed in the application overlay file :zephyr_file:`samples/subsys/modbus/rtu_client/app.overlay` The A+, B- lines of the RS-485 shields should be connected together. Alternatively UART RX,TX signals of two boards can be connected crosswise. Building and Running ******************** This sample can be found under :zephyr_file:`samples/subsys/modbus/rtu_client` in the Zephyr tree. The following commands build and flash RTU client sample. .. zephyr-app-commands:: :zephyr-app: samples/subsys/modbus/rtu_client :board: frdm_k64f :goals: build flash :compact: The example communicates with the RTU server and lets the LEDs light up one after the other. .. code-block:: console *** Booting Zephyr OS build zephyr-v2.3.0-1993-g07e8d80ae028 *** [00:00:00.005,000] mb_rtu: RTU timeout 2005 us [00:00:00.050,000] mbc_sample: WR|RD holding register: 48 00 65 00 6c 00 6c 00 6f 00 00 00 00 00 00 00 |H.e.l.l. o....... [00:00:00.062,000] mbc_sample: Coils state 0x00 [00:00:00.864,000] mbc_sample: Coils state 0x07 .. _`joy-it RS-485 shield for Arduino`: https://joy-it.net/en/products/ARD-RS485