Datasheet

Section 8 EXDMA Controller (EXDMAC)
Page 440 of 1384 R01UH0310EJ0500 Rev. 5.00
Sep 25, 2012
H8S/2426, H8S/2426R, H8S/2424 Group
(1) Transfer Requests from Multiple Channels (Except Auto Request Cycle Steal Mode)
If transfer requests for different channels are issued during a transfer operation, the highest-
priority channel (excluding the currently transferring channel) is selected. The selected channel
begins transfer after the currently transferring channel releases the bus. If there is a bus request
from a bus master other than the EXDMAC at this time, a cycle for the other bus master is
initiated. If there is no other bus request, the bus is released for one cycle.
Channel switching does not take place during a burst transfer or a block transfer of a single block.
Figure 8.13 shows a case in which transfer requests for channels 2 and 3 are issued
simultaneously. The example shown in the figure illustrates the handling of external requests in
the cycle steal mode.
Channel 2 transfer
φ
Idle
Bus
release
Address bus
EXDMA control
Channel 3 transfer
Channel 2 Channel 3
Channel 2
Request
held
Selected
Channel 3
Request cleared
Request cleared
Bus
release
Channel 2
Channel 3
Figure 8.13 Example of Channel Priority Timing
(2) Transfer Requests from Multiple Channels in Auto Request Cycle Steal Mode
If transfer requests for different channels are issued during a transfer in auto request cycle steal
mode, the operation depends on the channel priority. If the channel that made the transfer request
is of higher priority than the channel currently performing transfer, the channel that made the
transfer request is selected.
If the channel that made the transfer request is of lower priority than the channel currently
performing transfer, that channel's transfer request is held pending, and the currently transferring
channel remains selected.