Seagate Medalist Pro 4520, Руководство по эксплуатации продукта

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3.3 Synchronous DMA Transfer
3.3.1 Signal Line Definitions
Some existing ATA signal lines are redefined during the Synchronous
DMA protocol to provide new functions. If the Synchronous DMA transfer
mode was previously chosen by the Set Features, the ATA signal lines
change from the old to new definitions as soon as the host allows for a
DMA burst. The drive detects this change upon assertion of the –DMACK
line. These lines revert back to their original definitions upon the deas-
sertions of –DMACK at the termination of the DMA burst.
Signal Line Definitions
Pin New Definitions Old Definitions
21
DMARQ DMARQ
29
–DMACK –DMACK
27
25
–DMACK
IORDY on write commands
–DIOR on read commands
25
27
STROBE –DIOR on write commands
IORDY on read commands
23 STOP –DIOW
Note. DMARQ and –DMACK signal lines remain unchanged. This en-
sures backward compatibility with PIO modes.
3.3.2 Protocol Rules
The general rules of the Synchronous DMA Transfer Protocol are as
follows:
•
A DMA burst is defined as the period from an assertion of –DMACK
to subsequent deassertion of –DMACK.
•
A receiver must be prepared to receive at least two words of data
whenever it enters or resumes a burst mode.
•
During the entire burst, –CS0, –CS1, and –IOCS16 are in the high
negated state. DA2, DA1, and DA0 are driven low.
•
The drive begins driving and stops tristating IORDY when –DMACK
is first asserted and SyncDMA is enabled. The drive must continue to
36 Medalist Pro 9140, 6530 and 4520 Product Manual, Rev. B