
DR
AFT
DR
AFT
DRAFT
DR
D
RAFT
DRAFT
DRA
FT DRAF
D
RAFT DRAFT DRAFT DRAFT DRAFT D
DRAFT
D
RAFT DRA
FT DRAFT DRAFT DRAFT DRA
UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
277 of 808
NXP Semiconductors
UM10360
Chapter 14: LPC17xx UART0/2/3
THRE = 1 and there have not been at least two characters in the UnTHR at one time
since the last THRE = 1 event. This delay is provided to give the CPU time to write data to
UnTHR without a THRE interrupt to decode and service. A THRE interrupt is set
immediately if the UARTn THR FIFO has held two or more characters at one time and
currently, the UnTHR is empty. The THRE interrupt is reset when a UnTHR write occurs or
a read of the UnIIR occurs and the THRE is the highest interrupt (UnIIR[3:1] = 001).
4.6 UARTn FIFO Control Register (U0FCR - 0x4000 C008, U2FCR -
0x4009 8008, U3FCR - 0x4009 C008, Write Only)
The UnFCR controls the operation of the UARTn Rx and TX FIFOs.
4.6.1 DMA Operation
The user can optionally operate the UART transmit and/or receive using DMA. The DMA
mode is determined by the DMA Mode Select bit in the FCR register. This bit only has an
affect when the FIFOs are enabled via the FIFO Enable bit in the FCR register.
Table 256: UARTn FIFO Control Register (U0FCR - address 0x4000 C008,
U2FCR - 0x4009 8008, U3FCR - 0x4007 C008, Write Only) bit description
Bit
Symbol
Value
Description
Reset Value
0
FIFO Enable 0
UARTn FIFOs are disabled. Must not be used in the
application.
0
1
Active high enable for both UARTn Rx and TX
FIFOs and UnFCR[7:1] access. This bit must be set
for proper UART operation. Any transition on this bit
will automatically clear the related UART FIFOs.
1
RX FIFO
Reset
0
No impact on either of UARTn FIFOs.
0
1
Writing a logic 1 to UnFCR[1] will clear all bytes in
UARTn Rx FIFO, reset the pointer logic. This bit is
self-clearing.
2
TX FIFO
Reset
0
No impact on either of UARTn FIFOs.
0
1
Writing a logic 1 to UnFCR[2] will clear all bytes in
UARTn TX FIFO, reset the pointer logic. This bit is
self-clearing.
3
DMA Mode
Select
When the FIFO enable bit (bit 0 of this register) is
set, this bit selects the DMA mode. See
0
5:4
-
-
Reserved, user software should not write ones to
reserved bits. The value read from a reserved bit is
not defined.
NA
7:6
RX Trigger
Level
These two bits determine how many receiver
UARTn FIFO characters must be written before an
interrupt or DMA request is activated.
0
00
Trigger level 0 (1 character or 0x01)
01
Trigger level 1 (4 characters or 0x04)
10
Trigger level 2 (8 characters or 0x08)
11
Trigger level 3 (14 characters or 0x0E)