Write Data Buffer Function; Write Data Buffer Function For External Data Bus - Renesas H8SX/1650 Hardware Manual

6.13

Write Data Buffer Function

6.13.1

Write Data Buffer Function for External Data Bus

This LSI has a write data buffer function for the external data bus. Using the write data buffer
function enables external writes and internal accesses in parallel. The write data buffer function is
made available by setting the WDBE bit to 1 in BCR1.
Figure 6.40 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 continues for two cycles or longer, and there is
an internal access next, an external write only is executed in the first two cycles. However, from
the next cycle onward, internal accesses (on-chip memory or internal I/O register read/write) and
the external address space write rather than waiting until it ends are executed in parallel.
Iφ
Internal
address bus
Bφ
A23 to A0
External
CSn
space
write
LHWR, LLWR
D15 to D0
Figure 6.40 Example of Timing when Write Data Buffer Function is Used
On-chip memory read
External write cycle
On-chip
memory 1
T1
External address
Section 6 Bus Controller (BSC)
Peripheral module read
On-chip
Peripheral module address
memory 2
T2
Rev.2.00 Jun. 28, 2007 Page 211 of 666
T3
REJ09B0311-0200