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4.4.5
Wait Control
When accessing external space, the H8S/2678 Series chip can extend the bus cycle by inserting
one or more wait states (T
). There are two ways of inserting wait states: (1) program wait
w
insertion and (2) pin wait insertion using the WAIT pin.
Program Wait Insertion: From 0 to 3 wait states can be inserted automatically between the T
2
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
state is inserted. If the WAIT pin is held low, T
of ø in the last T
or T
state, another T
states
2
w
w
w
are inserted until it goes high.
This is useful when inserting seven or more T
states, or when changing the number of T
states to
w
w
be inserted for different external devices.
The WAITE bit setting applies to all areas.
Figure 4.17 shows an example of wait state insertion timing.
134
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