HD6432633 Datasheet, PDF (287/1453 Pages) Renesas Technology Corp – Series of Microcomputers (MCUs: microcomputer units)

7.9 Write Data Buffer Function
The H8S/2633 Series has a write data buffer function in the external data bus. Using the write data
buffer function enables external writes and DMA single address mode transmission 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 7-38 shows an example of the timing when the write data buffer function is used. When
this function is used, if an external write and DMA single address mode transmission 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.
On-chip memory read Internal I/O register read
External write cycle
T₁
T₂
T_W
T_W
T₃
Internal address bus
Internal read signal
Internal memory Internal I/O register address
A23 to A0
External address
External
space
write
CSn
HWR, LWR
D15 to D0
Figure 7-38 Example of Timing when Write Data Buffer Function is Used
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