
XR16L651
2.5V, 3.3V AND 5V LOW POWER UART WITH 32-BYTE FIFO
REV. P1.0.0
á
PRELIMINARY
24
CTS# is by a change of state on the input pin with
auto flow control enabled, EFR bit-7, and depend-
ing on selection on MCR bit-2.
RTS# is when its receiver changes the state of the
output pin during auto RTS flow control enabled by
EFR bit-6 and selection of MCR bit-2.
6.4.2
Interrupt Clearing:
LSR interrupt is cleared by a read to the LSR regis-
ter.
RXRDY and RXRDY Time-out are cleared by read-
ing data until FIFO falls below the trigger level.
TXRDY interrupt is cleared by a read to the ISR
register.
MSR interrupt is cleared by a read to the MSR reg-
ister.
Xoff or Special character interrupt is cleared by a
read to ISR.
RTS# and CTS# status change interrupts are
cleared by a read to the MSR register.
ISR[0]: Interrupt Status
Logic 0 = An interrupt is pending and the ISR con-
tents may be used as a pointer to the appropriate in-
terrupt service routine.
Logic 1 = No interrupt pending. (default condition)
ISR[3:1]: Interrupt Status
These bits indicate the source for a pending interrupt
at interrupt priority levels 1, 2, 3 and 4 (See Interrupt
Source Table 9).
ISR[5:4]: Interrupt Status
These bits are enabled when EFR bit-4 is set to a log-
ic 1. ISR bit-4 indicates that the receiver detected a
data match of the Xoff character(s).
N
OTE
:
Note that once set to a logic 1, the ISR bit-4 will stay
a logic 1 until a Xon character is received. ISR bit-5 indi-
cates that CTS# or RTS# has changed state.
ISR[7:6]: FIFO Enable Status
These bits are set to a logic 0 when the FIFOs are
disabled. They are set to a logic 1 when the FIFOs
are enabled.
6.5
This register is used to enable the FIFOs, clear the
FIFOs, set the transmit/receive FIFO trigger levels,
and select the DMA mode. The DMA, and FIFO
modes are defined as follows:
FCR BIT-0: TX and RX FIFO Enable
Logic 0 = Disable the transmit and receive FIFO. (de-
fault).
Logic 1 = Enable the transmit and receive FIFOs.
This bit must be set to logic 1 when other FCR bits
are written or they will not be programmed.
FCR[1]: RX FIFO Reset
This bit is only active when FCR bit-0 is a ‘1’.
Logic 0 = No receive
FIFO
reset. (default)
Logic 1 = Reset the receive FIFO pointers and FIFO
level counter logic (the receive shift register is not
cleared or altered). This bit will return to a logic 0 after
resetting the FIFO.
FCR[2]: TX FIFO Reset
This bit is only active when FCR bit-0 is a ‘1’.
Logic 0 = No transmit FIFO reset. (default)
FIFO C
ONTROL
R
EGISTER
(FCR)
T
ABLE
9: I
NTERRUPT
S
OURCE
AND
P
RIORITY
L
EVEL
P
RIORITY
ISR R
EGISTER
S
TATUS
B
ITS
S
OURCE
OF
INTERRUPT
+
L
EVEL
B
IT
-5
B
IT
-4
B
IT
-3
B
IT
-2
B
IT
-1
B
IT
-0
1
0
0
0
1
1
0
LSR (Receiver Line Status Register)
2
0
0
0
1
0
0
RXRDY (Received Data Ready)
3
0
0
1
1
0
0
RXRDY (Receive Data Time-out)
4
0
0
0
0
1
0
TXRDY ( Transmitter Holding Register Empty)
5
0
0
0
0
0
0
MSR (Modem Status Register)
6
0
1
0
0
0
0
RXRDY (Received Xoff or Special character)
7
1
0
0
0
0
0
CTS#/DSR#, RTS#/DTR# change of state
-
0
0
0
0
0
1
None (default)