r4f2426 Renesas Electronics Corporation., r4f2426 Datasheet - Page 325

• Manufacturer Part Number: r4f2426
• Description: 16-bit Single-chip Microcomputer H8s Family / H8s/2400 Series
• Manufacturer: Renesas Electronics Corporation.

6.11
This LSI has a write data buffer function for the external data bus. Using the write data buffer
function enables external writes and DMA single address mode transfers to be executed in parallel
with internal accesses. The write data buffer function is made available by setting the WDBE bit
to 1 in BCR.
Figure 6.95 shows an example of the timing when the write data buffer function is used. When this
function is used, if an external address space write or DMA single address mode transfer continues
for two states or longer, and there is an internal access next, an external write only is executed in
the first state, but from the next state onward an internal access (on-chip memory or internal I/O
register read/write) is executed in parallel with the external address space write rather than waiting
until it ends.
External space
write
Figure 6.95 Example of Timing when Write Data Buffer Function Is Used
Write Data Buffer Function
Internal address bus
Internal read signal
HWR, LWR
D15 to D0
A23 to A0
CSn
φ
T
1
On-chip memory read Internal I/O register read
T
Internal memory
2
External write cycle
External address
Rev. 1.00 Sep. 19, 2008 Page 297 of 1270
T
W
Internal I/O register address
Section 6 Bus Controller (BSC)
T
W
T
3
REJ09B0466-0100