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Wait Mode in Areas Where Wait-State Controller is Disabled
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External three-state access areas in which the wait-state controller is disabled (ASTn = 1, WCEn =
0) operate in pin wait mode 0. The other wait modes are unavailable. The settings of bits WMS1
and WMS0 are ignored in these areas.
Pin Wait Mode 0: Wait states can only be inserted by WAIT pin control. During access to an
external three-state-access area, if the WAIT pin is low at the fall of the system clock (ø) in the T
) is inserted. If the WAIT pin remains low, wait states continue to be
state, a wait state (T
W
inserted until the WAIT signal goes high. Figure 6-12 shows the timing.
ø
WAIT
pin
Address bus
AS
RD
Read
access
Data bus
HWR
, LWR
Write
access
Data bus
Note:
Arrows indicate time of sampling of the
*
Inserted by
T
T
1
2
*
External address
WAIT
pin.
Figure 6-12 Pin Wait Mode 0
134
WAIT
signal
T
T
W
W
*
*
Read data
Write data
2
T
3
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