LPC47N237-MD SMSC [SMSC Corporation], LPC47N237-MD Datasheet - Page 31

• Manufacturer Part Number: LPC47N237-MD
• Description: 3.3V I/O CONTROLLER FOR PORT REPLICATORS AND DOCKING STATIONS
• Manufacturer: SMSC [SMSC Corporation]

3.3v I/O Controller for Port Replicators and Docking Stations
8.1.5
SMSC DS – LPC47N237
Bit 0
Setting this bit to a logic "1" enables both the XMIT and RCVR FIFOs. Clearing this bit to a logic "0"
disables both the XMIT and RCVR FIFOs and clears all bytes from both FIFOs. When changing from FIFO
Mode to non-FIFO (16450) mode, data is automatically cleared from the FIFOs. This bit must be a 1 when
other bits in this register are written to or they will not be properly programmed.
Bit 1
Setting this bit to a logic "1" clears all bytes in the RCVR FIFO and resets its counter logic to 0. The shift
register is not cleared. This bit is self-clearing.
Bit 2
Setting this bit to a logic "1" clears all bytes in the XMIT FIFO and resets its counter logic to 0. The shift
register is not cleared. This bit is self-clearing.
Bit 3
Writing to this bit has no effect on the operation of the UART. DMA modes are not supported in this chip.
Bit 4,5
Reserved
Bit 6,7
These bits are used to set the trigger level for the RCVR FIFO interrupt.
Interrupt Identification Register (IIR)
Address Offset = 2H, DLAB = X, READ
By accessing this register, the host CPU can determine the highest priority interrupt and its source. Four
levels of priority interrupt exist. They are in descending order of priority:
1.
2.
3.
4.
Information indicating that a prioritized interrupt is pending and the source of that interrupt is stored in the
Interrupt Identification Register (refer to Interrupt Control Table). When the CPU accesses the IIR, the
Serial Port freezes all interrupts and indicates the highest priority pending interrupt to the CPU. During this
Receiver Line Status (highest priority)
Received Data Ready
Transmitter Holding Register Empty
MODEM Status (lowest priority)
BIT 7
0
0
1
1
DATASHEET
BIT 6
0
1
0
1
Page 31
TRIGGER LEVEL (BYTES)
RCVR FIFO
14
1
4
8
Revision 0.3 (10-26-04)