LPC47M192 datasheet(70/228 Pages) SMSC

70 / 228 page

SMSC DS – LPC47M192

Page 70

Rev. 03/30/05

DATASHEET

operational but the interrupts’ sources are now the lower four bits of the MODEM Control Register instead of the

MODEM Control inputs. The interrupts are still controlled by the Interrupt Enable Register.

Bits 5 through 7

These bits are permanently set to logic zero.

LINE STATUS REGISTER (LSR)

Address Offset = 5H, DLAB = X, READ/WRITE

Bit 0

Data Ready (DR). It is set to a logic “1” whenever a complete incoming character has been received and transferred

into the Receiver Buffer Register or the FIFO. Bit 0 is reset to a logic “0” by reading all of the data in the Receive

Buffer Register or the FIFO.

Bit 1

Overrun Error (OE). Bit 1 indicates that data in the Receiver Buffer Register was not read before the next character

was transferred into the register, thereby destroying the previous character. In FIFO mode, an overrun error will

occur only when the FIFO is full and the next character has been completely received in the shift register, the

character in the shift register is overwritten but not transferred to the FIFO. The OE indicator is set to a logic “1”

immediately upon detection of an overrun condition, and reset whenever the Line Status Register is read.

Bit 2

Parity Error (PE). Bit 2 indicates that the received data character does not have the correct even or odd parity, as

selected by the even parity select bit. The PE is set to a logic “1” upon detection of a parity error and is reset to a

logic “0” whenever the Line Status Register is read. In the FIFO mode this error is associated with the particular

character in the FIFO it applies to. This error is indicated when the associated character is at the top of the FIFO.

Bit 3

Framing Error (FE). Bit 3 indicates that the received character did not have a valid stop bit. Bit 3 is set to a logic “1”

whenever the stop bit following the last data bit or parity bit is detected as a zero bit (Spacing level). The FE is reset

to a logic “0” whenever the Line Status Register is read. In the FIFO mode this error is associated with the particular

character in the FIFO it applies to. This error is indicated when the associated character is at the top of the FIFO.

The Serial Port will try to resynchronize after a framing error. To do this, it assumes that the framing error was due to

the next start bit, so it samples this ‘start’ bit twice and then takes in the ‘data’.

Bit 4

Break Interrupt (BI). Bit 4 is set to a logic “1” whenever the received data input is held in the Spacing state (logic “0”)

for longer than a full word transmission time (that is, the total time of the start bit + data bits + parity bits + stop bits).

The BI is reset after the CPU reads the contents of the Line Status Register. In the FIFO mode this error is

associated with the particular character in the FIFO it applies to. This error is indicated when the associated character

is at the top of the FIFO. When break occurs only one zero character is loaded into the FIFO. Restarting after a

break is received, requires the serial data (RXD) to be logic “1” for at least ½ bit time.

Note:

Bits 1 through 4 are the error conditions that produce a Receiver Line Status Interrupt whenever any of the

corresponding conditions are detected and the interrupt is enabled.

Bit 5

Transmitter Holding Register Empty (THRE). Bit 5 indicates that the Serial Port is ready to accept a new character

for transmission. In addition, this bit causes the Serial Port to issue an interrupt when the Transmitter Holding

Transmitter Holding Register into the Transmitter Shift Register. The bit is reset to logic “0” whenever the CPU loads

the Transmitter Holding Register. In the FIFO mode this bit is set when the XMIT FIFO is empty, it is cleared when at

least 1 byte is written to the XMIT FIFO. Bit 5 is a read only bit.

Bit 6

Transmitter Empty (TEMT). Bit 6 is set to a logic “1” whenever the Transmitter Holding Register (THR) and

Transmitter Shift Register (TSR) are both empty. It is reset to logic “0” whenever either the THR or TSR contains a

data character. Bit 6 is a read only bit. In the FIFO mode this bit is set whenever the THR and TSR are both empty,

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