HD6432646 Hitachi, HD6432646 Datasheet - Page 212

• Manufacturer Part Number: HD6432646
• Description: (HD64F264x Series) 16-Bit Microcomputer
• Manufacturer: Hitachi

7.7
The H8S/2646 Series 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.
178
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
T
1
On-chip memory read Internal I/O register read
T
Internal memory
2
External write cycle
External address
T
W
Internal I/O register address
T
W
T
3