Intel 386 Manuale Utente Pagina 343

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Intel386™ EX EMBEDDED MICROPROCESSOR USERS MANUAL
12-8
Figures 12-2 and 12-3 are simple diagrams of how the Temporary Register is filled and emptied
for a Read DMA cycle and a Write DMA cycle.
Figure 12-2. DMA Temporary Buffer Operation for a Read Transfer
Figure 12-3. DMA Temporary Buffer Operation for A Write Transfer
A3381-01
Filling the Temporary Register
DREQ
n
#1
DREQ
n
#2
DREQ
n
#3
DREQ
n
#4
Emptying the Temporary Register
Write
#1
Write
#1
Write
#1
Write
#1
Four separate requests each with a read
of the requester. Each byte is stored in
the Temporary Register.
Once the Temporary Resister is full, the
DMA does four burst writes to the target
to empty it.
A3382-01
Filling the Temporary Register
DREQ
n
#1
Emptying the Temporary Register
A single request with four separate reads of
the target. Each read stores a byte in the
Temporary Register.
Once the Temporary Resister is full, the
DMA does a write cycle to transfer the first
byte from the Temporary Register to the
target. On each subsequent request, the
DMA performs a write cycle transferring a
byte from the Temporary Register to the
target. This continues until empty.
DREQ
n
#2
DREQ
n
#3
DREQ
n
#4
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