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Section 6 Bus Controller (BSC)
6.5.6
Wait Control
When accessing the external address space, this LSI can extend the bus cycle by inserting one or
more wait states (T
). There are three ways of inserting wait states: Program wait insertion, pin
W
wait insertion using the WAIT pin, and the combination of program wait and the WAIT pin.
(1)
In Normal Extended Mode
(a)
Program Wait Mode
A specified number of wait states T
accessing the external address space. The number of wait states T
the WC1 and WC0 bits in WSCR (the WC11 and WC10 bits in WSCR2 for the 256-Kbyte
extended area).
(b)
Pin Wait Mode
A specified number of wait states T
accessing the external address space. The number of wait states T
the WC1 and WC0 bits. If the WAIT pin is low at the falling edge of φ in the last T
state is inserted. If the WAIT pin is held low, T
another T
W
Pin wait mode is useful when inserting four or more T
states to be inserted for each external device.
(c)
Pin Auto-Wait Mode
A specified number of wait states T
the external address space if the WAIT pin is low at the falling edge of φ in the last T
number of wait states T
pin is held low, T
states are inserted only up to the specified number of states.
W
Pin auto-wait mode enables the low-speed memory interface only by inputting the chip select
signal to the WAIT pin.
Figure 6.28 shows an example of wait state insertion timing in pin wait mode.
The settings after a reset are: 3-state access, 3 program wait insertion, and WAIT pin input
disabled.
Rev. 1.00 Mar. 12, 2008 Page 148 of 1178
REJ09B0403-0100
are always inserted between the T
W
are always inserted between the T
W
are inserted between the T
W
is specified by the settings of the WC1 and WC0 bits. Even if the WAIT
W
state and T
2
is specified by the settings of
W
state and T
2
is specified by the settings of
W
states are inserted until it goes high.
W
states, or when changing the number of T
W
state and T
2
state when
3
state when
3
or T
state,
2
W
state when accessing
3
state. The
2
W
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