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Rev. 1.00
444 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)
RTS Flow Control
In the RTS flow control, the USART RTS pin is active with a logic low state when the receive data
register is empty. It means that the receiver is ready to receive a new data. When the RX FIFO reaches
the trigger level which is specified by configuring the RXTL field in the USRFCR register, the USART
RTS pin is inactive with a logic high state. Figure 166 shows the example of RTS flow control.
Start Bit
Bit 0 Bit 1 Bit 2 Bit 3 Bit 4
Bit N
Parity Bit
Stop Bit
Start Bit
N = 6 ~ 8
Idle
Bit 0 Bit 1 Bit 2 Bit 3
Bit 4
Bit N
Parity Bit
Stop Bit
N = 6 ~ 8
RXFS[3:0]
3
4
0
1
RTS
Read data until RX FIFO is empty
Reach the RX trigger level
RXTL[1:0] = b10
Figure 166. USART RTS Flow Control
CTS Flow Control
If the hardware flow control function is enabled, the URTXEN bit in the USRCR register will be
controlled by the USART CTS input signal. If the USART CTS pin is forced to a logic low state,
the URTXEN bit will automatically be set to 1 to enable the data transmission. However, if the
USART CTS pin is forced to a logic high state, the URTXEN bit will be cleared to 0 and then the
data transmission will also be disabled.
When the USART CTS pin is forced to a logic high state during a data transmission period, the
current data transmission will be continued until the stop bit is completed. The Figure
167 shows
an example of communication with CTS flow control.
Start Bit
Bit 0 Bit 1 Bit 2 Bit 3 Bit 4
Bit N
Parity Bit
Stop Bit
Start Bit
N = 6 ~ 8
Idle
Bit 0
Bit 1 Bit 2 Bit 3 Bit 4
Bit N
Parity Bit
Stop
Bit
N = 6 ~ 8
TXFS[3:0]
4
3
2
CTS
Start Bit
Bit 0
Figure 167. USART CTS Flow Control
IrDA
The USART IrDA mode is provided for half-duplex point-to-point wireless communication.
The USART module includes an integrated modulator and demodulator which allow a wireless
communication using infrared transceivers. The transmitter specifies a logic data ‘0’ as a ‘high’
pulse and a logic data ‘1’ as a ‘low’ level while the receiver specifies a logic data ‘0’ as a ‘low’ pulse
and a logic data ‘1’ as ‘high’ level in the IrDA mode.