h8s-2172 Renesas Electronics Corporation., h8s-2172 Datasheet - Page 219

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

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 DMAC 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 7.14 shows examples of transfer timing in cases that include auto request cycle steal mode.
Address bus
DMA control
Channel 0
Channel 1
Channel 2
φ
Idle
Request
Request
Request cleared
held
held
Figure 7.13 Example of Channel Priority Timing
Channel 0
Selected
selected
Not
Request
Channel 0 transfer
Request cleared
held
Channel 0
Channel 1
Selected
release
Bus
Channel 1 transfer
Request cleared
Channel 1
Rev. 2.00, 03/04, page 187 of 534
Channel 2
release
Bus
Channel 2 transfer
Channel 2