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6.5.4
Wait Control
When accessing external space, this LSI can extend the bus cycle by inserting one or more wait
states (T
). There are two ways of inserting wait states: program wait insertion and pin wait
w
insertion using the WAIT pin.
Program Wait Insertion: From 0 to 7 wait states can be inserted automatically between the T
state and T
state on an individual area basis in 3-state access space, according to the settings in
3
WTCRA and WTCRB.
Pin Wait Insertion: Setting the WAITE bit to 1 in BCR enables wait input by means of the
WAIT pin. When external space is accessed in this state, a program wait is first inserted in
accordance with the settings in WTCRA and WTCRB. If the WAIT pin is low at the falling edge
of φ in the last T
or T
2
inserted until it goes high. This is useful when inserting seven or more T
the number of T
states to be inserted for different external devices. The WAITE bit setting
w
applies to all areas. Figure 6.17 shows an example of wait state insertion timing.
The settings after a reset are: 3-state access, insertion of 7 program wait states, and WAIT input
disabled.
Rev. 2.00, 05/03, page 148 of 820
state is inserted. If the WAIT pin is held low, T
state, another T
w
w
states are
w
states, or when changing
w
2
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