Section 7 DMA Controller (DMAC)
Rev. 3.00 Mar. 14, 2006 Page 189 of 804
REJ09B0104-0300
Figure 7.31 shows an example of block transfer mode activated by the
DREQ
signal low level.
The
DREQ
signal is sampled every cycle from the next rising edge of the B
φ
signal immediately
after the DTE bit write cycle.
When a low level of the
DREQ
signal is detected while a transfer request by the
DREQ
signal is
enabled, a transfer request is held in the DMAC. When the DMAC is activated, the transfer
request is cleared. Receiving the next transfer request resumes after completion of the write cycle
and then a low level of the
DREQ
signal is detected. This operation is repeated until the transfer is
completed.
Wait
Wait
Wait
Min. of 3 cycles
Min. of 3 cycles
Transfer
source
Transfer
destination
Transfer
destination
Transfer
source
Read
Write
Read
Write
Bus released
Bus released
Bus released
DMA read
cycle
DMA write
cycle
DMA read
cycle
DMA write
cycle
B
φ
DREQ
Address bus
DMA
operation
Channel
[1]
[2]
[3]
[4]
[5]
[6]
[7]
Transfer request enable resumed
Transfer request enable resumed
[1]
After DMA transfer request is enabled, a low level of the
DREQ
signal is detected at the rising edge of the B
φ
signal and a transfer
request is held.
[2][5] The DMAC is activated and the transfer request is cleared.
[3][6] A DMA cycle is started.
[4][7] Transfer request enable is resumed after completion of the write cycle.
(A low level of the
DREQ
signal is detected at the rising edge of the B
φ
signal and a transfer request is held. This is the same as [1].)
1-block transfer
1-block transfer
Request
Request
Duration of transfer
request disabled
Duration of transfer
request disabled
Figure 7.31 Example of Transfer in Block Transfer Mode Activated
by
DREQ
Low Level
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Содержание H8SX series
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