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17-16 Intel® PXA255 Processor Developer’s Manual
Hardware UART
17.5.7 Receive FIFO Occupancy Register (FOR)
The FOR, shown in Table 17-11, shows the number of bytes currently remaining in the receive
FIFO. It can be used by the processor to determine the number of trailing bytes to remove. The
FOR is incremented once for each byte of data written to the receive FIFO and decremented once
for each byte read.
This is a read/write register. Ignore reads from reserved bits. Write zeros to reserved bits.
1 RESETRF
Reset Receiver FIFO – When RESETRF is set to 1, all the bytes in the receiver FIFO are
cleared. The DR bit in the LSR is reset to 0. All the error bits in the FIFO and the FIFOE bit
in the LSR are cleared. Any error bits, OE, PE, FE or BI, that had been set in LSR are still
set. The receiver shift register is not cleared. If the IIR had been set to received data
available, it is cleared.
0 = Writing 0 has no effect
1 = The receiver FIFO is cleared
0TRFIFOE
Transmit and Receive FIFO Enable – TRFIFOE enables/disables the transmitter and
receiver FIFOs. When TRFIFOE = 1, both FIFOs are enabled (FIFO Mode). When
TRFIFOE = 0, the FIFOs are both disabled (non-FIFO Mode). Writing a 0 to this bit clears
all bytes in both FIFOs. When changing from FIFO mode to non-FIFO mode and vice versa,
data is automatically cleared from the FIFOs. This bit must be 1 when other bits in this
register are written or the other bits are not programmed.
0 = FIFOs are disabled
1 = FIFOs are enabled
Table 17-10. FCR Bit Definitions (Sheet 2 of 2)
Physical Address
0x4160_0008
FIFO Control Register (FCR) PXA255 Processor Hardware 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
TIL
RESETTF
RESETRF
TRFIFOE
Reset ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 0 0 ? ? 0 0 0 0
Bits Name Description
Table 17-11. FOR Bit Definitions
Physical Address
0x4160_0024
FIFO Occupancy Register (FOR) PXA255 Processor Hardware 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 Byte Count
Reset
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 0 0 0 0 0 0 0
Bits Name Description
31:7 — reserved
6:0 Byte Count Number of bytes (0-64) remaining in the receiver FIFO