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UM008101-0601 Direct Memory Access

Bus Release on Match

When the DMA is programmed to stop (release the bus) on match in Burst

or Continuous modes, a match causes BUSREQ to go inactive on the next

DMA operation, for example, at the end of the next read in search-only,

simultaneous transfer/searches, or at the end of the following write in

sequential transfer or transfer/searches (Figure 68).

Figure 68. Bus Release on Match (Burst and Continuous Modes)

Because of the pipelining scheme, matches are determined while the next

DMA read or write is being performed. Table 12 lists the number of bytes

transferred in any class or mode.

The RDY line can go inactive after the matching operation begins without

affecting this bus-release timing. However, the time at which RDY goes

inactive can affect the number of bytes transferred, as described in Table 11

and Figure 32.

Bus Release on Not Ready

Burst mode, when RDY goes inactive, causes BUSREQ to go High on the

next rising edge of CLK after the completion of its current byte operation,

for example, at the end of the current read in search-only, simultaneous

transfer/search, or at the end of the following write in sequential transfer/

BUSREQ

RDY

Byte n DMA

Inactive

Read in

Byte n+1

and

on Byte n

Read in

Match Found

Active

Inactive

CLK

1 2 ... 175 176 177 178 179 180 181 182 183 184 185 ... 329 330

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