Intel PXA26X User Manual download pdf (Page 382)

10-16 Intel® PXA26x Processor Family Developer’s Manual

Universal Asynchronous Receiver/Transmitter

Table 10-13. Line Status Register – LSR (Sheet 1 of 2)

Base+0x14 Line Status 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

FIFOE

TEMT

TDRQ

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 1 1 0 0 0 0 0

Read only

Bits Name Description

31:8 — Reserved

7FIFOE

FIFO ERROR STATUS:

In non-FIFO mode, this bit is 0. In FIFO Mode, FIFOE is set to 1 when there is at least one

parity error, framing error, or break indication for any of the characters in the FIFO. A

processor read to the LSR does not reset this bit. FIFOE is reset when all erroneous

characters have been read from the FIFO. If DMA requests are enabled (IER bit 7 is set to

1) and FIFOE is set to 1, the error interrupt is generated and no receive DMA request is

generated even when the receive FIFO reaches the trigger level. Once the errors have

been cleared by reading the FIFO, DMA requests are re-enabled automatically. If DMA

requests are not enabled (IER bit7 is set to 0), FIFOE set to 1 does not generate an error

interrupt.

0 – No FIFO or no errors in receiver FIFO

1 – At least one character in receiver FIFO has errors

6TEMT

TRANSMITTER EMPTY:

Set when the Transmit Holding Register and the Transmitter Shift Register are both empty.

It is cleared when either the Transmit Holding Register or the Transmitter Shift Register

contains a data character. In FIFO mode, TEMT is set when the transmitter FIFO and the

Transmit Shift Register are both empty.

0 – There is data in the Transmit Shift Register, the Transmit Holding Register, or the FIFO

1 – All the data in the transmitter has been shifted out

5TDRQ

TRANSMIT DATA REQUEST:

Indicates that the UART is ready to accept a new character for transmission. In addition,

this bit causes the UART to issue an interrupt to the processor when the transmit data

request interrupt enable is set high and generates the DMA request to the DMA controller if

DMA requests and FIFO mode are enabled. The TDRQ bit is set when a character is

transferred from the Transmit Holding Register into the Transmit Shift Register. The bit is

cleared with the loading of the Transmit Holding Register. In FIFO mode, TDRQ is set to 1

when half of the characters in the FIFO have been loaded into the Shift register or the

RESETTF bit in FCR has been set. It is cleared when the FIFO has more than half data. If

more than 64 characters are loaded into the FIFO, the excess characters are lost.

0 – There is data in THR or FIFO waiting to be shifted out

1 – Transmit FIFO has half or less than half data

4BI

BREAK INTERRUPT:

Set when the received data input is held low for longer than a full word transmission time

(that is, the total time of Start bit + data bits + parity bit + stop bits). The Break indicator is

reset when the processor reads the LSR. In FIFO mode, only one character equal to 0x00,

is loaded into the FIFO regardless of the length of the break condition. BI shows the break

condition for the character at the front of the FIFO, not the most recently received

character.

0 – No break signal has been received

1 – Break signal received

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