xr16m780 Exar Corporation, xr16m780 Datasheet - Page 19

• Manufacturer Part Number: xr16m780
• Description: 1.62v To 3.63v High Performance Uart With 64-byte Fifo
• Manufacturer: Exar Corporation

REV. 1.0.0
transmission as soon as the stop bit of the character in process is shifted out. Transmission is resumed after
the CTS# input is re-asserted (LOW), indicating more data may be sent.
F
IGURE
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.
13. A
UTO
(RXA FIFO
CTSB#
RXA FIFO
Interrupt)
RTSA#
TXB
INTA
Trigger Reached
RTS
Receiver FIFO
Trigger Level
Local UART
Transmitter
Auto CTS
Auto RTS
UARTA
Monitor
AND
Data Starts
Receive
Data
CTS F
Assert RTS# to Begin
1
2
Transmission
Trigger Level
3
LOW
4
RX FIFO
RTSA#
TXA
CTSA#
RXA
ON
1.62V TO 3.63V HIGH PERFORMANCE UART WITH 64-BYTE FIFO
C
ON
ONTROL
5
O
7
PERATION
RTS High
Threshold
19
6
8
OFF
Suspend
OFF
RTSB#
CTSB#
Threshold
RTS Low
RXB
TXB
Restart
9
10
11
Trigger Reached
ON
Remote UART
Trigger Level
Receiver FIFO
12
Auto CTS
Auto RTS
Transmitter
UARTB
Monitor
ON
Trigger Level
RX FIFO
RTSCTS1
XR16M780