h8s-2172 Renesas Electronics Corporation., h8s-2172 Datasheet - Page 182

• Manufacturer Part Number: h8s-2172
• Description: Renesas 16-bit Single-chip Microcomputer H8s Family H8s-2100 Series
• Manufacturer: Renesas Electronics Corporation.

6.8
Write Data Buffer Function
This LSI 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
to 1 in BCR.
Figure 6.50 shows an example of the timing when the write data buffer function is used. When this
function is used, if an external address space 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 address space write rather than waiting
until it ends.
On-chip memory read Internal I/O register read
External write cycle
T
T
T
T
T
1
2
W
W
3
φ
Internal
Internal
Internal I/O
Internal address bus
memory 1
memory 2
register address
Internal read signal
External address
A19 to A0
External space
write
,
D15 to D0
Note: n = 3 to 0
Figure 6.50 Example of Timing when Write Data Buffer Function is Used
Rev. 2.00, 03/04, page 150 of 534