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NUC970 Technical Reference Manual
Publication Release Date: Dec. 15, 2015
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Revision V1.30
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Auto-Flow Control
5.16.5.4
The UART controllers support auto-flow control function that uses two low-level signals, CTSn (clear-
to-send) and RTSn (request-to-send) to control the flow of data transfer between the UART and
external devices (ex: Modem). When auto-flow is enabled, the UART is not allowed to receive data
until the UART asserts RTSn (RTSn high) to external device. When the number of bytes in the RX-
FIFO equals the value of RTS_TRI_LEV (UART_TLCTL[13:12]), the RTSn is de-asserted. The UART
sends data out when UART controller detects CTSn is asserted (CTSn high) from external device. If a
valid asserted CTSn is not detected the UART controller will not send data out. The auto-flow function
is implemented in High-speed UART only.
The following diagram demonstrates the auto-flow control block diagram.
APB BUS
TX
CTSn
RX
RTSn
Parallel to Serial
Flow Control
Serial to Parallel
Flow Control
TX FIFO
RX FIFO
Figure 5.16-5 UART Auto-Flow Control Block Diagram
Wake-Up Function
5.16.5.5
The UART Controller supports wake-up system function. The wake-up source includes CTSn, RIn,
DCD and DSR signals. All High-speed UART support CTSn signal, but only UART1 supports all full
modem wake-up ports.
In power condition, when the WAKE_CTS_EN(UA_CTL[8]) is set and the toggle of CTSn pin can
wake-up the system.
Case 1:
Figure 5.16-6 UART CTSn Wake-Up Case 1
Case 2:
sleep mode
CLK
CTSn
WAKE_SYSTEM
INT_WAKE