Renesas ZTAT H8S/2357F, Hardware Manual

Page: 164 / 1047

Rev.6.00 Oct.28.2004 page 136 of 1016
REJ09B0138-0600H
6.4.5 Wait Control
When accessing external space, the H8S/2357 Group can extend the bus cycle by inserting one or more wait states (T
w
).
There are two ways of inserting wait states: program wait insertion and 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
3
state on an
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
2
or T
w
state, a T
w
state is inserted. If the
WAIT
pin is held low, T
w
states are inserted until it goes
high.
This is useful when inserting four or more T
w
states, or when changing the number of T
w
states for different external
devices.
The WAITE bit setting applies to all areas.