h8s-2646 Renesas Electronics Corporation., h8s-2646 Datasheet - Page 203

• Manufacturer Part Number: h8s-2646
• Description: Renesas 16-bit Single-chip Microcomputer H8s Family/h8s/2600 Series
• Manufacturer: Renesas Electronics Corporation.

7.7
The H8S/2646 Group has a write data buffer function in the external data bus. Using this 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 in BCRL to 1.
Figure 7.18 shows an example of the timing when the write data buffer function is used. When this
function is used, if an external write continues for 2 states or longer, and there is an internal access
next, only an external write 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 write rather than waiting until it ends.
External
space
write
Internal address bus
Internal read signal
Figure 7.18 Example of Timing when Write Data Buffer Function is Used
Write Data Buffer Function
HWR, LWR
D15 to D0
A23 to A0
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1
On-chip memory read Internal I/O register read
T
Internal memory
2
External write cycle
External address
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T
W
Internal I/O register address
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W
Section 7 Bus Controller
REJ09B0257-0500
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3