Datasheet

Section 8 EXDMA Controller (EXDMAC)
R01UH0309EJ0500 Rev. 5.00 Page 455 of 1408
Sep 24, 2012
H8S/2456, H8S/2456R, H8S/2454 Group
(3) EDREQ Pin Falling Edge Activation Timing
Figure 8.26 shows an example of single address mode transfer activated by the EDREQ pin falling
edge.
EXDMA
single
cycle
Address bus
φ
EDREQ
Idle
Bus release
EXDMA control
Channel
Transfer source/
destination
Transfer source/
destination
Bus release
Idle
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] EXDMA 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
EXDMA
single
cycle
Figure 8.26 Example of Single Address Mode Transfer Activated
by 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 EXDMA 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.