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M0A21/M0A23 Series
May 06, 2022
Page
432
of 746
Rev 1.02
M0
A21
/M
0
A
2
3
SE
RIES
TEC
H
NICAL
RE
FEREN
C
E
M
ANUAL
nRTS to external device. When the number of bytes stored in the RX FIFO equals the value of
RTSTRGLV (UART_FIFO[19:16]), the nRTS is de-asserted. The UART sends data out when UART
detects nCTS is asserted from external device. If the valid asserted nCTS is not detected, the UART
will not send data out. The auto flow control block diagram is shown in Figure 6.11-11.
APB BUS
RX FIFO
TX FIFO
Flow Control
Serial to Parallel
Serial to Parallel
UART_nCTS
UART_RXD
UART_nRTS
UART_TXD
Figure 6.11-11 Auto-Flow Control Block Diagram
Figure 6.11-12 demonstrates the nCTS auto-flow control of UART function mode. User must set
ATOCTSEN (UART_INTEN[13]) to enable nCTS auto-flow control function. The CTSACTLV
(UART_MODEMSTS[8]) can set nCTS pin input active state. The CTSDETF (UART_MODEMSTS[0])
is set when any state change of nCTS pin input has occurred, and then TX data will be automatically
transmitted from TX FIFO.
nCTS pin input
Active
nCTS pin input status of UART function mode
D0
D1
D2
D3
D4
D5
D6
D7
P
Start
bit
Stop
bit
TX pin output
MODEMINT interrupt
Clear by softwave
Clear by softwave
Idle
Idle
TX output
delay
(default)
CTSSTS
UART_MODEMSTS[4]
CTSACTLV=0
CTSACTLV=1
CTSDETF
MODEMINT interrupt
TX stop
Inactive
Figure 6.11-12 UART nCTS Auto-Flow Control Enabled
As shown in Figure 6.11-13, in UART nRTS auto-flow control mode (ATORTSEN
(UART_INTEN[12])=1), the nRTS internal signal is controlled by UART FIFO controller with RTSTRGLV
(UART_FIFO[19:16]) trigger level.
Setting RTSACTLV (UART_MODEM[9]) can control the nRTS pin output is inverse or non-inverse from
nRTS signal. User can read the RTSSTS (UART_MODEM[13]) bit to get real nRTS pin output voltage