HD6412332 RENESAS [Renesas Technology Corp], HD6412332 Datasheet - Page 223

• Manufacturer Part Number: HD6412332
• Description: Renesas 16-Bit Single-Chip Microcomputer H8S Family/H8S/2300 Series
• Manufacturer: RENESAS [Renesas Technology Corp]

6.9
The chip 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
in BCRL to 1.
Figure 6.36 shows an example of the timing when the write data buffer function is used. When this
function is used, if an external 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 write rather than waiting until it ends.
External
space
write
Note: n = 0 to 7
Internal address bus
Internal read signal
Figure 6.36 Example of Timing when Write Data Buffer Function is Used
Write Data Buffer Function
A
CS
HWR, LWR
D
23
15
n
to A
to D
0
0
T
1
On-chip memory read
Internal memory
T
2
External write cycle
External address
Rev.4.00 Sep. 07, 2007 Page 193 of 1210
T
W
Internal I/O register
T
register read
W
Internal I/O
address
REJ09B0245-0400
T
3