h8s-2649 Renesas Electronics Corporation., h8s-2649 Datasheet - Page 171

• Manufacturer Part Number: h8s-2649
• Description: Renesas 16-bit Single-chip Microcomputer H8s Family/h8s/2600 Series
• Manufacturer: Renesas Electronics Corporation.

7.8
This LSI has a write data buffer function for the external data bus. Using the write data buffer
function enables external writes to be executed in parallel with internal accesses. The write data
buffer function is made available by setting the WDBE bit to 1 in BCRL.
Figure 7.19 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 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 7.19 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
T
1
On-chip memory read Internal I/O register read
T
Internal memory
2
External write cycle
External address
T
Rev. 2.00 Dec. 05, 2005 Page 133 of 724
W
Internal I/O register address
Section 7 Bus Controller (BSC)
T
W
T
3
REJ09B0200-0200