LPC47N237-MD datasheet(35/138 Pages) SMSC

35 / 138 page

3.3v I/O Controller for Port Replicators and Docking Stations

SMSC DS – LPC47N237

Page 35

Revision 0.3 (10-26-04)

DATASHEET

Bit 1

This bit controls the Request To Send (nRTS) output. Bit 1 affects the nRTS output in a manner identical

to that described above for bit 0.

Bit 2

This bit controls the Output 1 (OUT1) bit. This bit does not have an output pin and can only be read or

written by the CPU.

Bit 3

Output 2 (OUT2). This bit is used to enable an UART interrupt. When OUT2 is a logic "0", the serial port

interrupt output is forced to a high impedance state - disabled. When OUT2 is a logic "1", the serial port

interrupt outputs are enabled.

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:

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.

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.

8.1.8

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

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