HD6432633 Datasheet, PDF (363/1453 Pages) Renesas Technology Corp – Series of Microcomputers (MCUs: microcomputer units)

Figure 8-26 shows an example of DREQ level activated block transfer mode transfer.
ø
DREQ
Bus release
1 block transfer
DMA
read
DMA
right
DMA Bus
dead release
1 block transfer
DMA
read
DMA DMA Bus
right dead release
Address bus
Transfer
source
Transfer
destination
Transfer
source
Transfer
destination
DMA control
Idle
Read Write
Dead Idle Read Write
Dead
Channel
Request
Request clear period
Request
Request clear period
Minimum of 2 cycles
Minimum of 2 cycles
[1] [2] [3]
[4] [5] [6]
Idle
[7]
Acceptance resumes
Acceptance resumes
[1] Acceptance after transfer enabling; the DREQ pin low level is sampled on the rising
edge of ø, and the request is held.
[2] [5] The request is cleared at the next bus break, and activation is started in the DMAC.
[3] [6] The DMA cycle is started.
[4] [7] Acceptance is resumed after the dead cycle is completed.
(As in [1], the DREQ pin low level is sampled on the rising edge of ø, and the request is held.)
Note: In write data buffer mode, bus breaks from [2] to [7] may be hidden, and not visible.
Figure 8-26 Example of DREQ Level Activated Block Transfer Mode Transfer
DREQ pin sampling is performed every cycle, with the rising edge of the next ø cycle after the
end of the DMABCR write cycle for setting the transfer enabled state as the starting point.
When the DREQ pin low level is sampled while acceptance by means of the DREQ pin is
possible, the request is held in the DMAC. Then, when activation is initiated in the DMAC, the
request is cleared. After the end of the dead cycle, acceptance resumes, DREQ pin low level
sampling is performed again, and this operation is repeated until the transfer ends.
309