
Rev. 1.00
446 of 486
July 31, 2018
32-Bit Arm
®
Cortex
®
-M0+ MCU
HT32F50231/HT32F50241
21 Universal Synchronous
Asynchronous Receiver T
ransmitter (USART)
21 Universal Synchronous
Asynchronous Receiver T
ransmitter (USART)
T
IrDA_L
= 3 × IrDAPSC / CK_USART
Note:
T
IrDA_L
is the transmitted pulse width in the low-power mode.
The IrDAPSC filed is the IrDA prescaler value in the IrDA Control Register IrDACR.
The debounce behavior in the IrDA low-power receiving mode is similar to the IrDA normal mode.
For glitch detection, the low pulse of which the pulse width is shorter than 1
× (IrDAPSC / CK_
USART) should be discarded in the IrDA receiver demodulation. A valid low data is accepted if its
low pulse width is greater than 2
× (IrDAPSC / CK_USART) duration.
The IrDA physical layer specification specifies a minimum delay with a value of 10 ms between the
transmission and reception switch; and this IrDA receiver set-up time also should be managed by
the software.
Transmitter
Modulation
Receiver
Demodulation
IrDAEN
1
RX_Data
TX_Data
0
1
0
TX
RX
SEL
SEL
TXSEL
Figure 169. USART I/O and IrDA Block Diagram
RS485 Mode
The RS485 mode of the USART provides the data transmission on the 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.