HD6412320 RENESAS [Renesas Technology Corp], HD6412320 Datasheet - Page 327

• Manufacturer Part Number: HD6412320
• Description: Renesas 16-Bit Single-Chip Microcomputer H8S Family H8S-2300 Series
• Manufacturer: RENESAS [Renesas Technology Corp]

When the DREQ pin low level is sampled while acceptance by means of the DREQ pin is
possible, the request is held in the DMAC. Then, when activation is initiated in the DMAC, the
request is cleared. After the end of the single cycle, acceptance resumes, DREQ pin low level
sampling is performed again, and this operation is repeated until the transfer ends.
7.5.12
DMAC internal-to-external dual address transfers and single address transfers can be executed at
high speed using the write data buffer function, enabling system throughput to be improved.
When the WDBE bit of BCRL in the bus controller is set to 1, enabling the write data buffer
function, dual address transfer external write cycles or single address transfers and internal
accesses (on-chip memory or internal I/O registers) are executed in parallel. Internal accesses are
independent of the bus master, and DMAC dead cycles are regarded as internal accesses.
A low level can always be output from the TEND pin if the bus cycle in which a low level is to be
output is an external bus cycle. However, a low level is not output from the TEND pin if the bus
cycle in which a low level is to be output from the TEND pin is an internal bus cycle, and an
external write cycle is executed in parallel with this cycle.
Figure 7.33 shows an example of burst mode transfer from on-chip RAM to external memory
using the write data buffer function.
Figure 7.33 Example of Dual Address Transfer Using Write Data Buffer Function
Internal read signal
External address
Internal address
Write Data Buffer Function
HWR, LWR
TEND
φ
DMA
read
DMA
write
Section 7 DMA Controller (Not Supported in the H8S/2321)
DMA
read
DMA
write
Rev.6.00 Sep. 27, 2007 Page 297 of 1268
DMA
read
DMA
write
DMA
read
DMA
write
REJ09B0220-0600
DMA
dead