Section 7 DMA Controller (DMAC)
Rev. 3.00 Mar. 14, 2006 Page 195 of 804
REJ09B0104-0300
(5)
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 7.37 shows an example of single address 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 one cycle of the transfer
request duration inserted by NRD = 1 on completion of the single cycle and then a low level of the
DREQ
signal is detected. This operation is repeated until the transfer is completed.
Min. of 3 cycles
Min. of 3 cycles
DMA single
cycle
DMA single
cycle
B
φ
DREQ
Address bus
Channel
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[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 single 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].)
Transfer source/
Transfer destination
Bus
released
Bus
released
Transfer request
enable resumed
Transfer request
enable resumed
Transfer source/
Transfer destination
Request
Request
Duration of transfer
request disabled
Duration of transfer
request disabled
Duration of transfer request
disabled which is extended
by NRD
Duration of transfer request
disabled which is extended
by NRD
Bus
released
Figure 7.37 Example of Transfer in Single Address Mode Activated
by
DREQ
Low Level with NRD = 1
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