D M A M o d u l e

 

 

 

 

 

 

 

 

 

 

Bits

Access

Mnemonic

Reset

Description

 

 

 

 

BTE continued

 

 

The DMA delivers to the destination peripheral the

 

 

 

 

same number of bytes read from the source

 

 

 

 

peripheral, regardless of whether the destination

 

 

 

 

peripheral can support bursting. If the destination

 

 

 

 

peripheral cannot support bursting, the DMA

 

 

 

 

controller issues multiple bus cycles to complete

 

 

 

 

the data move.

 

 

 

 

When operating in memory-to-memory mode, the

 

 

 

 

SIZE field determines the size of each operand

 

 

 

 

moved. It is usually more efficient to use a size of

 

 

 

 

32 bits; different SIZE values are required,

 

 

 

 

however, when the address alignment boundaries

 

 

 

 

for the source and destination are mismatched. If

 

 

 

 

the starting source and destination boundaries are

 

 

 

 

not on longword boundaries, a size of 16 or 8 bits

 

 

 

 

is required. If the starting source or destination

 

 

 

 

boundaries are on odd-byte boundaries, a size of 8

 

 

 

 

bits is required.

 

 

 

 

 

D23

R/W

REQ

0

Channel request source

 

 

 

 

0

Internal peripheral

 

 

 

 

1

External peripheral

 

 

 

 

Allows DMA channels 3/5 and 4/6 to be attached

 

 

 

 

to either an internal or external peripheral. When an

internal peripheral is selected, the DMA channel is hardwired to the peripheral defined in Table 49, “DMA channel assignments,” on page 133.

DMA channels 3/5 interface with an external peripheral using handshaking signals multiplexed through PORTA.

When REQ is set to 0 in DMA channel 3 and set to 1 in DMA channel 5, DMA channel 5 is tied to the external DMA port through PORTA.

When REQ is set to 1 in DMA channel 3, that channel is tied to the external DMA port through PORTA, no matter the REQ bit setting in DMA channel 5.

Table 50: DMA Control register bit definition

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Image 153
Digi NS7520 manual Req, Channel request source