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80 lines
4.6 KiB
Markdown
80 lines
4.6 KiB
Markdown
# UART RS485 Echo Example
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(See the README.md file in the upper level 'examples' directory for more information about examples.)
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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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## How to use example
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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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#### Connect an external RS485 serial interface to an ESP32 board
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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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```
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--------------------------------------------------------------------------------------------------------------------------
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| ESP32 Interface | #define | Default ESP32 Pin | Default ESP32-S2 Pins | External RS485 Driver Pin |
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| ----------------------|--------------------|-----------------------|-----------------------|---------------------------|
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| Transmit Data (TxD) | CONFIG_MB_UART_TXD | GPIO23 | GPIO20 | DI |
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| Receive Data (RxD) | CONFIG_MB_UART_RXD | GPIO22 | GPIO19 | RO |
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| Request To Send (RTS) | CONFIG_MB_UART_RTS | GPIO18 | GPIO18 | ~RE/DE |
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| Ground | n/a | GND | GND | GND |
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--------------------------------------------------------------------------------------------------------------------------
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```
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Note: The GPIO22 - GPIO25 can not be used with ESP32-S2 chip because they are used for flash chip connection. Please refer to UART documentation for selected target.
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### Configure the project
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```
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idf.py menuconfig
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```
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### Build and Flash
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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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idf.py -p PORT 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 are 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. Once done there should be no any `.` displayed.
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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 hexadecimal form in the brackets.
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## Troubleshooting
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When example software does not show the `.` symbol, the issue is most likely related to connection errors of the 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 the appropriate serial port.
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