UM10503
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
958 of 1269
NXP Semiconductors
UM10503
Chapter 37: LPC43xx USART0_2_3
37.6.6.1 DMA Operation
The user can optionally operate the USART transmit and/or receive using DMA. The DMA
mode is determined by the DMA Mode Select bit in the FCR register. Note that for DMA
operation as for any operation of the USART, the FIFOs must be enabled via the FIFO
Enable bit in the FCR register.
USART receiver DMA
In DMA mode, the receiver DMA request is asserted when the receiver FIFO level
becomes equal to or greater than trigger level, or if a character time-out occurs. See the
description of the RX Trigger Level above. The receiver DMA request is cleared by the
DMA controller.
USART transmitter DMA
In DMA mode, the transmitter DMA request is asserted when the transmitter FIFO
transitions to not full. The transmitter DMA request is cleared by the DMA controller.
Table 829. USART FIFO Control Register Write Only (FCR - addresses 0x4008 1008
(USART0), 0x400C 1008 (USART2), 0x400C 2008 (USART3)) bit description
Bit
Symbol
Value Description
Reset
value
0
FIFOEN
FIFO Enable.
0
0
USART FIFOs are disabled. Must not be used in the application.
1
Active high enable for both USART Rx and TX FIFOs and
FCR[7:1] access. This bit must be set for proper USART
operation. Any transition on this bit will automatically clear the
USART FIFOs.
1
RXFIFO
RES
RX FIFO Reset.
0
0
No impact on either of USART FIFOs.
1
Writing a logic 1 to FCR[1] will clear all bytes in USART Rx FIFO,
reset the pointer logic. This bit is self-clearing.
2
TXFIFO
RES
TX FIFO Reset.
0
0
No impact on either of USART FIFOs.
1
Writing a logic 1 to FCR[2] will clear all bytes in USART TX FIFO,
reset the pointer logic. This bit is self-clearing.
3
DMAMO
DE
DMA Mode Select. When the FIFO enable bit (bit 0 of this
register) is set, this bit selects the DMA mode.
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
RXTRIG
LVL
RX Trigger Level.
These two bits determine how many receiver USART FIFO
characters must be written before an interrupt is activated.
0
0x0
Trigger level 0 (1 character or 0x01).
0x1
Trigger level 1 (4 characters or 0x04).
0x2
Trigger level 2 (8 characters or 0x08).
0x3
Trigger level 3 (14 characters or 0x0E).
31:8 -
-
Reserved
-