PXN20RM Datasheet, PDF (515/1376 Pages) Freescale Semiconductor, Inc – PXN20 Microcontroller

Peripheral Source #1
Peripheral Source #2
Peripheral Source #3
Always Disabled
Source #0
DMA Channel Multiplexer (DMA_MUX)
DMA Channel #n
n = 8 to 31
Peripheral Source #55
Always Enabled
Source #60
Always Enabled
Source #63
CHCONFIGn[SOURCE]
Figure 23-6. DMA_MUX Channel 8–31 Block Diagram
23.4.3 Always Enabled DMA Sources
In addition to the 55 peripherals that can be used as DMA sources, there are four additional DMA sources
that are always enabled. Unlike the peripheral DMA sources, where the peripheral controls the flow of data
during DMA transfers, the always enabled sources provide no such throttling of the data transfers. These
sources are most useful in the following cases:
• Doing DMA transfers to/from GPIO—Moving data from/to one or more GPIO pins, either
un-throttled (i.e.,as fast as possible), or periodically (using the DMA triggering capability).
• Doing DMA transfers from memory to memory—Moving data from memory to memory, typically
as fast as possible, sometimes with software activation.
• Doing DMA transfers from memory to the external bus (or vice-versa)—Similar to memory to
memory transfers, this is typically done as quickly as possible.
• Any DMA transfer that requires software activation—Any DMA transfer that should be explicitly
started by software.
In cases where software should initiate the start of a DMA transfer, an always enabled DMA source can
be used to provide maximum flexibility. When activating a DMA channel via software, subsequent
Freescale Semiconductor
PXN20 Microcontroller Reference Manual, Rev. 1
23-11