r4f2456 Renesas Electronics Corporation., r4f2456 Datasheet - Page 468

• Manufacturer Part Number: r4f2456
• Description: 16-bit Single-chip Microcomputer H8s Family / H8s/2400 Series
• Manufacturer: Renesas Electronics Corporation.

Section 8 EXDMA Controller (EXDMAC)
(3)
Figure 8.26 shows an example of single address mode transfer activated by the EDREQ pin falling
edge.
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, and EDREQ pin high level sampling for edge sensing is started. If EDREQ
pin high level sampling is completed by the end of the DMA single cycle, acceptance resumes
after the end of the single cycle, 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 438 of 1342
REJ09B0467-0100
[1]
[2], [5] Request is cleared at end of next bus cycle, and activation is started in EXDMAC.
[3], [6] DMA cycle start; EDREQ pin high level sampling is started at rise of φ.
[4], [7] When EDREQ pin high level has been sampled, acceptance is resumed after completion of single cycle.
Figure 8.26 Example of Single Address Mode Transfer Activated by EDREQ Pin Falling
EDREQ Pin Falling Edge Activation Timing
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.)
φ
EDREQ
Address bus
EDACK
DMA control
Channel
Idle
[1]
Minimum 3 cycles
Request
Bus release
[2]
clearance period
Single
[3]
Request
DMA single
Transfer source/
destination
Edge
Idle
Acceptance
resumed
[4]
Minimum 3 cycles
Request
Bus release
[5]
clearance period
Single
[6]
Request
Transfer source/
DMA single Bus release
destination
Idle
Acceptance
resumed
[7]