196
(3) Relationship between Chip Select (
CS
) Signal and Read (
RD
) Signal
Depending on the system’s load conditions, the
RD
signal may lag behind the
CS
signal. An
example is shown in figure 7-35.
In this case, with the setting for no idle cycle insertion (a), there may be a period of overlap
between the bus cycle A
RD
signal and the bus cycle B
CS
signal.
Setting idle cycle insertion, as in (b), however, will prevent any overlap between the
RD
and
CS
signals.
In the initial state after reset release, idle cycle insertion (b) is set.
T
1
Address bus
ø
RD
Bus cycle A
Data bus
T
2
T
3
T
1
T
2
Bus cycle B
Long output
floating time
Data
collision
T
1
Address bus
ø
RD
Bus cycle A
Data bus
T
2
T
3
T
I
T
1
Bus cycle B
T
2
HWR
HWR
CS
(area A)
CS
(area B)
CS
(area A)
CS
(area B)
(a) Idle cycle not inserted
(ICIS1 = 0)
(b) Idle cycle inserted
(Initial value ICIS1 = 1)
Figure 7-35 Relationship between Chip Select (
CS
) and Read (
RD
)