1.. zephyr:code-sample:: modbus-rtu-client
2   :name: Modbus RTU client
3   :relevant-api: modbus
4
5   Communicate with a Modbus RTU server.
6
7Overview
8********
9
10This is a simple application demonstrating a Modbus RTU client implementation
11in Zephyr RTOS.
12
13Requirements
14************
15
16This sample has been tested with the nRF52840-DK and FRDM-K64F boards,
17but it should work with any board that has a free UART interface.
18
19RTU client example is running on an evaluation board and communicates
20with another board running the :zephyr:code-sample:`modbus-rtu-server` sample.
21
22In addition to the evaluation board a RS-485 shield may be used.
23The shield converts UART TX, RX signals to RS-485.
24An Arduino header compatible shield like `joy-it RS-485 shield for Arduino`_
25can be used. This example uses DE signal, which is controlled by pin D9
26on the JOY-IT shield. For other shields, ``de-gpios`` property must be adapted
27or removed in the application overlay file
28:zephyr_file:`samples/subsys/modbus/rtu_client/app.overlay`
29
30The A+, B- lines of the RS-485 shields should be connected together.
31
32Alternatively UART RX,TX signals of two boards can be connected crosswise.
33
34Building and Running
35********************
36
37This sample can be found under
38:zephyr_file:`samples/subsys/modbus/rtu_client` in the Zephyr tree.
39
40The following commands build and flash RTU client sample.
41
42.. zephyr-app-commands::
43   :zephyr-app: samples/subsys/modbus/rtu_client
44   :board: frdm_k64f
45   :goals: build flash
46   :compact:
47
48The example communicates with the RTU server and lets the LEDs light up
49one after the other.
50
51.. code-block:: console
52
53   *** Booting Zephyr OS build zephyr-v2.3.0-1993-g07e8d80ae028  ***
54   [00:00:00.005,000] <inf> mb_rtu: RTU timeout 2005 us
55   [00:00:00.050,000] <inf> mbc_sample: WR|RD holding register:
56   48 00 65 00 6c 00 6c 00  6f 00 00 00 00 00 00 00 |H.e.l.l. o.......
57   [00:00:00.062,000] <inf> mbc_sample: Coils state 0x00
58   [00:00:00.864,000] <inf> mbc_sample: Coils state 0x07
59
60
61.. _`joy-it RS-485 shield for Arduino`: https://joy-it.net/en/products/ARD-RS485
62