Datasheet

Section 8 EXDMA Controller
Rev. 3.00 Mar 17, 2006 page 378 of 926
REJ09B0283-0300
After one byte or word has been transferred in response to one transfer request, the bus is released.
While the bus is released, one or more CPU, DMAC, or DTC bus cycles are initiated.
EDREQ
EDREQEDREQ
EDREQ Pin Falling Edge Activation Timing: Figure 8.26 shows an example of single address
mode transfer activated by the EDREQ pin falling edge.
DMA single
φ
Address bus
EDREQ
Idle
Bus release
DMA control
Channel
Transfer source/
destination
Transfer source/
destination
Bus release
Idle
DMA single
Bus release
Single Single Idle
EDACK
[1] [3][2] [4] [6][5] [7]
Acceptance
resumed
Acceptance
resumed
[1] Acceptance after transfer enabling; EDREQ pin low level is sampled at rise of φ, and request is held.
[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.
(As in [1], EDREQ pin low level is sampled at rise of φ, and request is held.)
Request
clearance period
Request
clearance period
Minimum 3 cycles
Request
Minimum 3 cycles
Request
Figure 8.26 Example of Single Address Mode Transfer Activated by EDREQ
EDREQEDREQ
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.