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Section 12 Bus State Controller (BSC)
Rev. 4.00 Sep. 14, 2005 Page 331 of 982
REJ09B0023-0400
12.5.4 CSn Assert Period Expansion
The number of cycles from CSn assertion to RD, WEn assertion can be specified by setting bits
SW1 and SW0 in CSnWCR. The number of cycles from RD, WEn negation to CSn negation can
be specified by setting bits HW1 and HW0. Therefore, a flexible interface to an external device
can be obtained. Figure 12.11 shows an example. A Th cycle and a Tf cycle are added before and
after an ordinary cycle, respectively. In these cycles, RD and WEn are not asserted, while other
signals are asserted. The data output is prolonged to the Tf cycle, and this prolongation is useful
for devices with slow writing operations.
T1
CKIO
A25 to A0
CSn
RD/WR
RD
D31 to D0
WEn
D31 to D0
BS
Th
Read
Write
T2
DACKn*
Tf
Note: * The waveform for DACKn is when active low is specified.
Figure 12.11 CSn Assert Period Expansion