r4f2456 Renesas Electronics Corporation., r4f2456 Datasheet - Page 456

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

Section 8 EXDMA Controller (EXDMAC)
(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.
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.
Figure 8.14 shows examples of transfer timing in cases that include auto request cycle steal mode.
Rev. 1.00 Sep. 19, 2008 Page 426 of 1342
REJ09B0467-0100