h8s-2172 Renesas Electronics Corporation., h8s-2172 Datasheet - Page 224

• Manufacturer Part Number: h8s-2172
• Description: Renesas 16-bit Single-chip Microcomputer H8s Family H8s-2100 Series
• Manufacturer: Renesas Electronics Corporation.

One block is transferred in response to one transfer request, and after the transfer, the bus is
released. While the bus is released, one or more CPU bus cycles are initiated.
DREQ Pin Falling Edge Activation Timing: Figure 7.20 shows an example of normal mode
transfer activated by the DREQ pin falling edge.
DREQ pin sampling is performed in each cycle starting at the next rise of φ after the end of the
DMMDR write cycle for setting the transfer-enabled state.
When a low level is sampled at the DREQ pin while acceptance via the DREQ pin is possible, the
request is held within the DMAC. Then when activation is initiated within the DMAC, the request
is cleared, and DREQ pin high level sampling for edge sensing is started. If DREQ pin high level
sampling is completed by the end of the DMA write cycle, acceptance resumes after the end of the
write cycle, and DREQ pin low level sampling is performed again; this sequence of operations is
repeated until the end of the transfer.
Figure 7.21 shows an example of block transfer mode transfer activated by the DREQ pin falling
edge.
Rev. 2.00, 03/04, page 192 of 534
φ
Address bus
DMA control
Channel
[1]
[2], [5] Request is cleared at end of next bus cycle, and activation is started in DMAC.
[3], [6] DMA cycle start;
[4], [7] When
Figure 7.20 Example of Normal Mode Transfer Activated by DREQ Pin Falling Edge
Acceptance after transfer enabling;
(As in [1],
Idle
[1]
Minimum 3 cycles
Request
pin high level has been sampled, acceptance is resumed after completion of write cycle.
Bus release
pin low level is sampled at rise of φ, and request is held.)
[2]
pin high level sampling is started at rise of φ.
Read
[3]
Request clearance period
Transfer source
DMA read
Write
DMA write
destination
Transfer
pin low level is sampled at rise of φ, and request is held.
Idle
Acceptance
resumed
[4]
Minimum 3 cycles
Request
Bus release
[5]
Read
[6]
Request clearance period
Transfer source
DMA read
Write
DMA write Bus release
destination
Transfer
Idle
Acceptance
resumed
[7]