Datasheet

Section 6 Bus Controller (BSC)
Rev.6.00 Mar. 18, 2009 Page 161 of 980
REJ09B0050-0600
6.5.4 Wait Control
When accessing external space, this LSI 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 7 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 in
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
2
or T
w
state, another 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 seven or more T
w
states, or when changing
the number of T
w
states to be inserted for different external devices. The WAITE bit setting
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.