Section 7 DMA Controller (DMAC)
Rev. 3.00 Mar. 14, 2006 Page 190 of 804
REJ09B0104-0300
(6)
Activation Timing by
DREQ
Low Level with NRD = 1
When the NRD bit in DMDR is set to 1, the timing of receiving the next transfer request is
delayed for one cycle.
Figure 7.32 shows an example of normal transfer mode activated by the
DREQ
signal low level
with NRD = 1.
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.
Duration of transfer
request disabled
Transfer
source
Transfer
destination
Transfer
destination
Transfer
source
Bus released
Bus released
Bus released
DMA read
cycle
DMA read
cycle
DMA read
cycle
DMA read
cycle
B
φ
DREQ
Address bus
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 one cycle 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].)
Request
Request
Min. of 3 cycles
Min. of 3 cycles
Duration of transfer request
disabled which is extended
by NRD
Duration of transfer request
disabled which is extended
by NRD
Duration of transfer
request disabled
Figure 7.32 Example of Transfer in Normal Transfer Mode Activated
by
DREQ
Low Level with NRD = 1
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