MAC7200 datasheet(566/976 Pages) FREESCALE

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Functional Description

MAC7200 Microcontroller Family Reference Manual, Rev. 2

488

Freescale Semiconductor

Figure 27-5. DMA Mux Channel Triggering: Ignored Trigger

This triggering capability may be used with any peripheral that supports DMA transfers, and is most useful

for two types of situations:

•

Periodically polling external devices on a particular bus. As an example, the transmit side of an SPI

is assigned to a DMA channel with a trigger, as described above. Once setup, the SPI will request

DMA transfers (presumably from memory) as long as its transmit buffer is empty. By using a

trigger on this channel, the SPI transfers can be automatically performed every 5

μs (as an

example). On the receive side of the SPI, the SPI and DMA can be configured to transfer receive

data into memory, effectively implementing a method to periodically read data from external

devices and transfer the results into memory without processor intervention.

•

Using the GPIO Ports to drive or sample waveforms. By configuring the DMA to transfer data to

one or more GPIO ports, it is possible to create complex waveforms using tabular data stored in

on-chip memory. Conversely, using the DMA to periodically transfer data from one or more GPIO

ports, it is possible to sample complex waveforms and store the results in tabular form in on-chip

memory.

A more detailed description of the capability of each trigger (i.e.-resolution, range of values, etc.) may be

found in Chapter 26, “Periodic Interrupt Timer (PIT_RTI)”.

27.4.2

DMA Channels 8-15

Channels 9–16 of the DMA Mux provide the normal routing functionality as described in Section 27.1.2,

“Modes of Operation.”

Periph Request

Trigger

DMA Request

MAC7200 Datasheet(PDF) 566 Page - Freescale Semiconductor, Inc