LPC47S457-NC SMSC [SMSC Corporation], LPC47S457-NC Datasheet - Page 68

• Manufacturer Part Number: LPC47S457-NC
• Description: Advanced I/O with X-Bus Interface
• Manufacturer: SMSC [SMSC Corporation]

Bit 4
This bit provides the loopback feature for diagnostic testing of the Serial Port. When bit 4 is set to logic "1", the following
occur:
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This feature allows the processor to verify the transmit and receive data paths of the Serial Port. In the diagnostic mode,
the receiver and the transmitter interrupts are fully operational. The MODEM Control Interrupts are also 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 overrunn 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 1/2 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.
SMSC DS – LPC47S45x
The TXD is set to the Marking State (logic "1").
The receiver Serial Input (RXD) is disconnected.
The output of the Transmitter Shift Register is "looped back" into the Receiver Shift Register input.
All MODEM Control inputs (nCTS, nDSR, nRI and nDCD) are disconnected.
The four MODEM Control outputs (nDTR, nRTS, OUT1 and OUT2) are internally connected to the four MODEM
Control inputs (nDSR, nCTS, RI, DCD).
The Modem Control output pins are forced inactive high.
Data that is transmitted is immediately received.
DATASHEET
Page 68 of 259
Rev. 07/09/2001