h8s-2172 Renesas Electronics Corporation., h8s-2172 Datasheet - Page 236

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

External Request/Cycle Steal Mode/Normal Transfer Mode: In external request mode, an
DMA transfer cycle is started a minimum of three cycles after a transfer request is accepted. The
next transfer request is accepted after the end of a one-transfer-unit DMA cycle. For external bus
space CPU cycles, at least two bus cycles are generated before the next DMA cycle.
If a transfer request is generated for another channel, an DMA cycle for the other channel is
generated before the next DMA cycle.
The DREQ pin sensing timing is different for low level sensing and falling edge sensing. The
same applies to transfer request acceptance and transfer start timing.
Figures 7.38 to 7.41 show operation timing examples for various conditions.
• No contention/dual address mode/low level sensing (see figure 7.38)
• CPU cycles/single address mode/low level sensing (see figure 7.39)
• No contention/single address mode/falling edge sensing (see figure 7.40)
• Contention with another channel/dual address mode/low level sensing (see figure 7.41)
Rev. 2.00, 03/04, page 204 of 534
φ pin
Bus cycle
Original
channel
Original
channel
Other
channel
transfer
request
(
)
Bus release
Figure 7.37 Auto Request/Burst Mode/Normal Transfer Mode
(Contention with Another Channel/Single Address Mode)
transfer cycle
DMA single
transfer cycle
DMA single
Last transfer
transfer cycle
DMA single
cycle
1 cycle
Bus
release
Other channel DMA cycle
release
Bus