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7.4.5
Wait Control
When accessing external space, the H8S/2633 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 and pin
w
wait insertion using the WAIT pin.
Program Wait Insertion
From 0 to 3 wait states can be inserted automatically between the T
state and T
state on an
2
3
individual area basis in 3-state access space, according to the settings of WCRH and WCRL.
Pin Wait Insertion
Setting the WAITE bit in BCRL to 1 enables wait insertion by means of the WAIT pin. Program
wait insertion is first carried out according to the settings in WCRH and WCRL. Then , if the
WAIT pin is low at the falling edge of ø in the last T
or T
state, a T
state is inserted. If the
2
w
w
WAIT pin is held low, T
states are inserted until it goes high.
w
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.
170
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