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7.4.5
Wait Control
When accessing external space, the H8S/2646 Series can extend the bus cycle by inserting one or
more wait states (T
). There are two ways of inserting wait states: program wait insertion.
w
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 of
3
WCRH and WCRL.
Pin Wait Insertion: Setting the WAITE bit in BCRH to 1 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 WCRH and WCRL. If the WAIT pin is low at the falling edge of ø
state is inserted. If the WAIT pin is held low, T
in the last T
or T
state, another T
states are
2
w
w
w
inserted until it goes high.
This is useful when inserting four or more T
states, or when changing the number of T
states for
w
w
different external devices.
The WAITE bit setting applies to all areas.
169
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