HD6412320 RENESAS [Renesas Technology Corp], HD6412320 Datasheet - Page 239

• Manufacturer Part Number: HD6412320
• 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 in 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 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.
Note: * The DMAC is not supported in the H8S/2321.
Note: n = 0 to 7
External
space
write
Internal address bus
Internal read signal
Figure 6.36 Example of Timing when Write Data Buffer Function is Used
Write Data Buffer Function
HWR, LWR
D
A
15
23
to D
to A
CSn
0
0
T
1
On-chip memory read Internal I/O register read
T
Internal memory
2
External write cycle
External address
Rev.6.00 Sep. 27, 2007 Page 209 of 1268
T
W
Internal I/O register address
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W
Section 6 Bus Controller
REJ09B0220-0600
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3