XR16M2551
18
HIGH PERFORMANCE LOW VOLTAGE DUART WITH 16-BYTE FIFO AND POWERSAVE FEATURE
REV. 1.0.2
FIGURE 10. AUTO RTS AND CTS FLOW CONTROL OPERATION
The local UART (UARTA) starts data transfer by asserting RTSA# (1). RTSA# is normally connected to CTSB# (2) of
remote UART (UARTB). CTSB# allows its transmitter to send data (3). TXB data arrives and fills UARTA receive FIFO
(4). When RXA data fills up to its receive FIFO trigger level, UARTA activates its RXA data ready interrupt (5) and con-
tinues to receive and put data into its FIFO. If interrupt service latency is long and data is not being unloaded, UARTA
monitors its receive data fill level to match the upper threshold of RTS delay and de-assert RTSA# (6). CTSB# follows
(7) and request UARTB transmitter to suspend data transfer. UARTB stops or finishes sending the data bits in its trans-
mit shift register (8). When receive FIFO data in UARTA is unloaded to match the lower threshold of RTS delay (9),
UARTA re-asserts RTSA# (10), CTSB# recognizes the change (11) and restarts its transmitter and data flow again until
next receive FIFO trigger (12). This same event applies to the reverse direction when UARTA sends data to UARTB
with RTSB# and CTSA# controlling the data flow.
RTSA#
CTSB#
RXA
TXB
Transmitter
Receiver FIFO
Trigger Reached
Auto RTS
Trigger Level
Auto CTS
Monitor
RTSA#
TXB
RXA FIFO
CTSB#
Remote UART
UARTB
Local UART
UARTA
ON
OFF
ON
Suspend
Restart
RTS High
Threshold
Data Starts
ON
OFF
ON
Assert RTS# to Begin
Transmission
1
2
3
4
5
6
7
Receive
Data
RTS Low
Threshold
9
10
11
Receiver FIFO
Trigger Reached
Auto RTS
Trigger Level
Transmitter
Auto CTS
Monitor
RTSB#
CTSA#
RXB
TXA
INTA
(RXA FIFO
Interrupt)
RX FIFO
Trigger Level
RX FIFO
Trigger Level
8
12
RTSCTS1