UM11029
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© NXP Semiconductors N.V. 2017. All rights reserved.
User manual
Rev. 1.0 — 16 June 2017
263 of 515
NXP Semiconductors
UM11029
Chapter 16: LPC84x DMA controller
16.5 General description
16.5.1 DMA requests and triggers
An operation on a DMA channel can be initiated by either a DMA request or a trigger
event. DMA requests come from peripherals and specifically indicate when a peripheral
either needs input data to be read from it, or that output data may be sent to it. DMA
requests are created by the UART, SPI, I2C, and DAC.
A trigger initiates a DMA operation and can be a signal from an unrelated peripheral.
Peripherals that generate triggers are the SCT, the ADC, and the analog comparator. In
addition, the DMA triggers also create a trigger output that can trigger DMA transactions
on another channel. Triggers can be used to send a character or a string to a UART or
other serial output at a fixed time interval or when an event occurs.
A DMA channel using a trigger can respond by moving data from any memory address to
any other memory address. This can include fixed peripheral data registers, or
incrementing through RAM buffers. The amount of data moved by a single trigger event
Fig 23. DMA block diagram
Configuration
AHB slave
interface
IRQ
complete
Arbiter
AHB
master
interface
active
clear
DMA
trigge rs
DMA
reque sts
Destination
address fetch
address cache
Source
address fetch
address cache
Control
Source
data
Destination
data
Reload
DMA_ITRIG_PINMUX0
25
13
DMA
trigge rs
DMA_ITRIG_PINMUX17
13
0
24
Channel