Section 7 DMA Controller (DMAC)
Rev. 3.00 Mar. 14, 2006 Page 187 of 804
REJ09B0104-0300
(4)
Activation Timing by
DREQ
Falling Edge
Figure 7.29 shows an example of normal transfer mode activated by the
DREQ
signal falling edge.
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 and starts detecting a high level of the
DREQ
signal for falling edge detection. If
a high level of the
DREQ
signal has been detected until completion of the DMA write cycle,
receiving the next transfer request resumes and then a low level of the
DREQ
signal is detected.
This operation is repeated until the transfer is completed.
Request
Wait
Wait
Wait
Request
Duration of transfer
request disabled
Duration of transfer
request disabled
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 and sampling the
DREQ
signal at the rising edge of the B
φ
signal is started to detect a high level of the
DREQ
signal.
[4][7] When a high level of the
DREQ
signal has been detected, 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].)
Figure 7.29 Example of Transfer in Normal Transfer Mode Activated
by
DREQ
Falling Edge
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