GD32A50x User Manual
478
RTS flow control
The USART receiver outputs the nRTS, which reflects the status of the receive buffer. When
data frame is received, the nRTS signal goes high to prevent the transmitter from sending
next frame. The nRTS signal keeps high when the receive buffer is full.
CTS flow control
The USART transmitter monitors the nCTS input pin to decide whether a data frame can be
transmitted. If the TBE bit in USART_STAT is ‘0’ and the nCTS signal is low, the transmitter
transmits the data frame. When the nCTS signal goes high during a transmission, the
transmitter stops after the current transmission is accomplished.
Figure 19-8. Hardware flow control
nCTS
RX
nRTS
RTS follow control
CTS follow control
TX
start
data2
start
data3
stop
stop
data1
stop
start
data1
Start
data2
stop
stop
USART_TDATA
data2
empty
empty
data3
empty
idle
idle
idle
idle
RS485 Driver Enable
The driver enable feature, which is enabled by setting bit DEM in the USART_CTL2 control
register, allows the user to activate the external transceiver control, through the DE (Driver
Enable) signal. The assertion time, which is programmed using the DEA [4:0] bits field in the
USART_CTL0 control register, is the time between the activation of the DE signal and the
beginning of the START bit. The de-assertion time, which is programmed using the DED [4:0]
bits field in the USART_CTL0 control register, is the time between the end of the last stop bit
and the de-activation of the DE signal. The polarity of the DE signal can be configured using
the DEP bit in the USART_CTL2 control register.
19.3.7.
Multi-processor communication
In multiprocessor communication, several USARTs are connected as a network. It will be a
big burden for a device to monitor all of the messages on the RX pin. To reduce the burden
of a device, software can put an USART module into a mute mode by writing 1 to the MMCMD
bit in USART_CMD register.
If a USART is in mute mode, all of the receive status bits cannot be set. The USART can also
be wake up by hardware by one of the three methods: idle frame method, address match
method and data match method.