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10-12 Intel® PXA26x Processor Family Developer’s Manual
Universal Asynchronous Receiver/Transmitter
10.4.2.6 FIFO Control Register (FCR)
The FCR is a write-only register that is located at the same address as the IIR, which is a read-only
register. The FCR enables/disables the transmitter/receiver FIFOs, clears the transmitter/receiver
FIFOs, and sets the receiver FIFO trigger level.
Table 10-10. Interrupt Identification Register Decode
Interrupt ID Bits Interrupt SET/RESET Function
3 2 1 0 Priority Type Source Cleared By...
0 0 0 1 — None No interrupt is pending —
0110Highest
Receiver Line
Status
Overrun error, parity error,
framing error, break
interrupt
Reading the LSR
0100
Second
Highest
Received Data
Available
Non-FIFO mode: Receive
buffer is full
FIFO mode: Trigger level
was reached
Non-FIFO mode: Reading
the Receiver Buffer
Register
FIFO mode: Reading bytes
until receiver FIFO drops
below trigger level or setting
FCR[RESETRF].
1100
Second
Highest
Character
Timeout
Indication
FIFO mode only: At least
one character is in the
receive FIFO and no data
has been sent for four
character times.
Reading the receiver FIFO,
setting FCR[RESETRF] or
a new start bit is received
0010
Third
Highest
Transmit FIFO
Data Request
Non-FIFO mode: Transmit
Holding Register empty
FIFO mode: Transmit has
half, or less than half, data
Non-FIFO mode: Reading
the IIR (if the source of the
interrupt) or writing into the
Transmit Holding Register
FIFO mode: Reading the
IIR Register (if the source of
the interrupt) or writing to
the transmitter FIFO
0000
Fourth
Highest
Modem Status
Clear to send, data set
ready, ring indicator, data
carrier detect
Reading the Modem Status
Register