r4f2426 Renesas Electronics Corporation., r4f2426 Datasheet - Page 462

• Manufacturer Part Number: r4f2426
• Description: 16-bit Single-chip Microcomputer H8s Family / H8s/2400 Series
• Manufacturer: Renesas Electronics Corporation.

Section 8 EXDMA Controller (EXDMAC)
EDREQ pin sampling is performed in each cycle starting at the next rise of φ after the end of the
EDMDR write cycle for setting the transfer-enabled state.
When a low level is sampled at the EDREQ pin while acceptance via the EDREQ pin is possible,
the request is held within the EXDMAC. Then when activation is initiated within the EXDMAC,
the request is cleared. At the end of the write cycle, acceptance resumes and EDREQ pin low level
sampling is performed again; this sequence of operations is repeated until the end of the transfer.
Rev. 1.00 Sep. 19, 2008 Page 434 of 1270
REJ09B0466-0100
Figure 8.21 Example of Block Transfer Mode Transfer Activated by EDREQ Pin Low Level
[1]
[2], [5] Request is cleared at end of next bus cycle, and activation is started in EXDMAC.
[3], [6] DMA cycle is started.
[4], [7] Acceptance is resumed after completion of dead cycle.
φ
EDREQ
Address bus
DMA control
Channel
Acceptance after transfer enabling; EDREQ pin low level is sampled at rise of φ, and request is held.
(As in [1], EDREQ pin low level is sampled at rise of φ, and request is held.)
Idle
[1]
Minimum 3 cycles
Request
Bus release
[2]
Read
Request clearance period
[3]
Transfer source
DMA read
One block transfer
Write
DMA write
destination
Transfer
Idle
Acceptance
resumed
[4]
Minimum 3 cycles
Request
Bus release
[5]
Read
Request clearance period
[6]
Transfer source
DMA read
One block transfer
Write
DMA write
destination
Transfer
Idle
Acceptance
resumed
[7]
Bus release