Espressif ESP32-S2 User Manual

Chapter 2. API Reference
(continued from previous page)
ESP | | RS485 bus side
RTS ------>| DE |
| A|----------<> A
+----| /RE |
| +-------x-------+
| |
GND GND
This circuit is preferable because it allows for collision detection and is quite simple at the same time. The receiver
in the line driver is constantly enabled, which allows the UART to monitor the RS485 bus. Echo suppression is per-
formed by the UART peripheral when the bit UART_RS485_CONF_REG.UART_RS485TX_RX_EN is enabled.
Circuit B: Manual Switching Transmitter/Receiver Without Collision Detection
VCC ---------------+
|
+-------x-------+
RXD <------| R |
| B|-----------<> B
TXD ------>| D ADM483 |
ESP | | RS485 bus side
RTS --+--->| DE |
| | A|-----------<> A
+----| /RE |
+-------x-------+
|
GND
This circuit does not allow for collision detection. It suppresses the null bytes that the hardware receives when
the bit UART_RS485_CONF_REG.UART_RS485TX_RX_EN is set. The bit UART_RS485_CONF_REG.
UART_RS485RXBY_TX_EN is not applicable in this case.
Circuit C: Auto Switching Transmitter/Receiver
VCC1 <-------------------+-----------+ +-------------------+----> VCC2
10K ____ | | | |
+---|____|--+ +---x-----------x---+ 10K ____ |
| | | +---|____|--+
RX <----------+-------------------| RXD | |
10K ____ | A|---+---------------<> A (+)
+-------|____|------| PV ADM2483 | | ____ 120
| ____ | | +---|____|---+ RS485␣
,→bus side
VCC1 <--+--|____|--+------->| DE | |
10K | | B|---+------------+--<> B (-)
---+ +-->| /RE | | ____
10K | | | | +---|____|---+
____ | /-C +---| TXD | 10K |
TX >---|____|--+_B_|/ NPN | | | |
|\ | +---x-----------x---+ |
| \-E | | | |
| | | | |
GND1 GND1 GND1 GND2 GND2
This galvanically isolated circuit does not require RTS pin control by a software application or driver because
it controls the transceiver direction automatically. However, it requires suppressing null bytes during transmis-
sion by setting UART_RS485_CONF_REG.UART_RS485RXBY_TX_EN to 1 and UART_RS485_CONF_REG.
UART_RS485TX_RX_EN to 0. This setup can work in any RS485 UART mode or even in UART_MODE_UART.
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Release v4.4

Espressif ESP32-S2 Specifications

General

Brand	Espressif
Model	ESP32-S2
Category	Single board computers
Language	English