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Rev. 1.00
475 of 576
January 28, 2022
32-Bit Arm
®
Cortex
®
-M0+ MCU
HT32F54231/HT32F54241/HT32F54243/HT32F54253
22 Universal Synchronous
Asynchronous Receiver T
ransmitter (USART)
22 Universal Synchronous
Asynchronous Receiver T
ransmitter (USART)
Transmitter
Modulation
Receiver
Demodulation
IrDAEN
1
RX_Data
TX_Data
0
1
0
TX
RX
SEL
SEL
TXSEL
Figure 176. USART I/O and IrDA Block Diagram
RS485 Mode
The RS485 mode of USART provides the data transmission on interface transmitted over a 2-wire
twisted pair bus. The RS485 transceiver interprets the voltage levels of the differential signals with
respect to a third common voltage. Without this common reference, the transceiver may interpret
the differential signals incorrectly. This enhances the noise rejection capabilities of the RS485
interface. The USART RTS pin is used to control the external RS485 transceiver whose polarity
can be selected by configuring the TXENP bit in the RS485 Control Register, named RS485CR,
when the USART operates in the RS485 mode.
RS485 Auto Direction Mode – AUD
When the RS485 mode is configured as a master transmitter, it will operate in the Auto Direction
Mode, AUD. In the AUD mode the polarity of the USART RTS pin is configurable according to the
TXENP bit in the RS485 Control Register in the RS485 mode. This pin can be used to control the
external RS485 transceiver to enable the transmitter.