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Preliminary
S3C2451X RISC MICROPROCESSOR
DMA CONTROLLER
9-5
Preliminary product information describe products that are in development,
for which full characterization data and associated errata are not yet available.
Specifications and information herein are subject to change without notice.
Demand/Handshake Mode Comparison
–
Related to the Protocol between XnXDREQ and XnXDACK
These are two different modes related to the protocol between XnXDREQ and XnXDACK. Figure. 9-2 shows the
differences between these two modes i.e., Demand and Handshake modes.
At the end of one transfer (Single/Burst transfer), DMA checks the state of double-synched XnXDREQ.
Demand mode
•
If XnXDREQ remains asserted, the next transfer starts immediately. Otherwise it waits for XnXDREQ to be
asserted.
Handshake mode
•
If XnXDREQ is deasserted, DMA deasserts XnXDACK in 2cycles. Otherwise it waits until XnXDREQ is
deasserted.
Caution: XnXDREQ has to be asserted (low) only after the deassertion (high) of XnXDACK.
Demand Mode
XSCLK
XnXDACK
XnXDACK
XnXDREQ
XnXDREQ
2cycles
Double
synch
Handshake Mode
BUS Acquisiton
1st Transfer
2nd Transfer
2cycles
Double
synch
2cycles
Actual Transfer
Read
Write
Read
Write
Read
Write
Figure 9-2. Demand/Handshake Mode Comparison