HD6412320 RENESAS [Renesas Technology Corp], HD6412320 Datasheet - Page 319

• Manufacturer Part Number: HD6412320
• Description: Renesas 16-Bit Single-Chip Microcomputer H8S Family H8S-2300 Series
• Manufacturer: RENESAS [Renesas Technology Corp]

DREQ Level Activation Timing (Normal Mode): Set the DTA bit for the channel for which the
DREQ pin is selected to 1.
Figure 7.25 shows an example of DREQ level activated normal mode transfer.
DREQ pin sampling is performed every cycle, with the rising edge of the next φ 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 write cycle, acceptance resumes, DREQ pin low level
sampling is performed again, and this operation is repeated until the transfer ends.
[1]
[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 write cycle is completed.
Note: In write data buffer mode, bus breaks from [2] to [7] may be hidden, and not visible.
DREQ
Address
bus
DMA
control
Channel
φ
Acceptance after transfer enabling; the DREQ pin low level is sampled on the rising edge of φ,
and the request is held.
(As in [1], the DREQ pin low level is sampled on the rising edge of φ, and the request is held.)
Figure 7.25 Example of DREQ Level Activated Normal Mode Transfer
Idle
[1]
Request
of 2 cycles
release
Minimum
Bus
[2]
Read
[3]
Request clear period
Transfer source
DMA
read
Write
Section 7 DMA Controller (Not Supported in the H8S/2321)
Transfer destination
Acceptance resumes
DMA
write
Idle
[4]
Request
of 2 cycles
Minimum
release
Rev.6.00 Sep. 27, 2007 Page 289 of 1268
Bus
[5]
Read
[6]
Request clear period
Transfer source Transfer destination
DMA
read
Write
Acceptance resumes
REJ09B0220-0600
DMA
write
Idle
[7]
release
Bus