Filter
Top Products
10-12 Intel® PXA255 Processor Developer’s Manual
UARTs
10.4.2.6 FIFO Control Register (FCR)
The FCR, shown in Table 10-11, 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.
This is a write-only register. Write zeros to reserved bits.
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 Register (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
Table 10-10. Interrupt Identification Register Decode (Sheet 2 of 2)
Interrupt ID Bits Interrupt SET/RESET Function
Table 10-11. FCR Bit Definitions (Sheet 1 of 2)
Base+0x08 FIFO Control Register UART
Bit
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
reserved
ITL
reserved
reserved
reserved
RESETTF
RESETRF
TRFIFOE
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Bits Name Description
31:8 — reserved
7:6 ITL
Interrupt Trigger Level: When the number of bytes in the receiver FIFO equals the interrupt
trigger level programmed into this field and the Received Data Available Interrupt is
enabled via the IER, an interrupt is generated and appropriate bits are set in the IIR. The
receive DMA request is also generated when the trigger level is reached.
0b00 – 1 byte or more in FIFO causes interrupt (Not valid in DMA mode)
0b01 – 8 bytes or more in FIFO causes interrupt and DMA request
0b10 – 16 bytes or more in FIFO causes interrupt and DMA request
0b11 – 32 bytes or more in FIFO causes interrupt and DMA request
5:3 — reserved