An existing UART driver does not support RS485 half duplex mode. This task adds this functionality to ESP_IDF UART driver. driver/uart.c/h: updated to add support of RS485 half duplex mode examples/peripherals/uart_echo_rs485/main/rs485_example.c: added test example components/driver/test/test_uart.c: added test of RS485 half duplex mode docs/en/api-reference/peripherals/uart.rst: updated documentation test_uart.c: suppress GCC warnings about discarded const qualifiers uart.rst: remove sphinx warning - "Duplicate explicit target name" simple change in uart.h file update (test_uart.c) after rebase from master update uart.rst, uart.c, rs485_example.c Update example description in file Readme.md update uart.c/h, uart.rst, test_uart.c according to review results update uart.h (uart_set_rx_timeout() description test_uart.c remove ignore tag uart.c/h: fix param errors test_uart.c: Remove GCC warning supress uart.rst: fix the notes rs485_example.c: fix output uart.c: remove reset using UART_RXFIFO_RST from driver. readme.md: Update example description The tests are completed using RS485 adapters hardware connected to two ESP32 WROVER KITs. TW#13812 Closes https://github.com/espressif/esp-idf/pull/667 Closes https://github.com/espressif/esp-idf/pull/1006
77 lines
4 KiB
Markdown
77 lines
4 KiB
Markdown
# UART RS485 Echo Example
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This is an example which echoes any data it receives on UART2 back to the sender in the RS485 network.
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It uses ESP-IDF UART software driver in RS485 half duplex transmission mode and requires external connection of bus drivers.
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The approach demonstrated in this example can be used in user application to transmit/receive data in RS485 networks.
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## Hardware required :
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PC + USB Serial adapter connected to USB port + RS485 line drivers + ESP32 WROVER-KIT board.
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The MAX485 line driver is used for example below but other similar chips can be used as well.
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### RS485 example connection circuit schematic:
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```
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VCC ---------------+ +--------------- VCC
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+-------x-------+ +-------x-------+
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RXD <------| RO | | RO|-----> RXD
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| B|---------------|B |
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TXD ------>| DI MAX485 | \ / | MAX485 DI|<----- TXD
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ESP32 WROVER-KIT | | RS-485 side | | SERIAL ADAPTER SIDE
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RTS --+--->| DE | / \ | DE|---+
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| | A|---------------|A | |
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+----| /RE | | /RE|---+-- RTS
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+-------x-------+ +-------x-------+
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--- ---
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```
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## How to setup and use an example:
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### Connect an external RS485 serial interface to an ESP32 board.
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```
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----------------------------------------------------------------------
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| ESP32 Interface | #define | ESP32 Pin | External RS485 |
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| ----------------------|---------------|-----------| Driver Pin |
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| Transmit Data (TxD) | ECHO_TEST_TXD | GPIO23 | DI |
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| Receive Data (RxD) | ECHO_TEST_RXD | GPIO22 | RO |
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| Request To Send (RTS) | ECHO_TEST_RTS | GPIO18 | ~RE/DE |
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| Ground | n/a | GND | GND |
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----------------------------------------------------------------------
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```
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Connect USB to RS485 adapter to computer and connect its D+, D- output lines with the D+, D- lines of RS485 line driver connected to ESP32 (See picture above).
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### Configure the application
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```
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make menuconfig
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```
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* Set serial port under Serial Flasher Options to the serial port of ESP32 WROVER-KIT board.
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### Build and flash software
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Build the project and flash it to the board, then run monitor tool to view serial output:
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```
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make -j4 flash monitor
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```
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(To exit the serial monitor, type ``Ctrl-]``.)
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See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.
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### Setup external terminal software
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Refer to the example and set up a serial terminal program to the same settings as of UART in ESP32 WROVER-KIT BOARD.
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Open the external serial interface in the terminal. By default if no any symbols received the application sends character "." to check transmission side.
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When typing message and push send button in the terminal you should see the message "RS485 Received: [ your message ], where your message is the message you sent from terminal.
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Verify if echo indeed comes from ESP32 by disconnecting either 'TxD' or 'RxD' pin. There should be no any "." once TxD pin is disconnected.
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## Example Output
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Example output of the application:
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```
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I (655020) RS485_ECHO_APP: Received 12 bytes:
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[ 0x79 0x6F 0x75 0x72 0x20 0x6D 0x65 0x73 0x73 0x61 0x67 0x65 ]
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```
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The received message is showed in HEX form in the brackets.
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## Troubleshooting
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Most of the issues when example software does not show the '.' symbol related to connection errors of external RS485 interface.
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Check the RS485 interface connection with the environment according to schematic above and restart the application.
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Then start terminal software and open appropriate serial port.
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