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6.5.4
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/CPWAIT pin, and the combination of program wait and the
WAIT/CPWAIT pin.
Program Wait Mode: A specified number of wait states T
between the T
state and T
2
the settings of the WC1 and WC0 bits in WSCR (the WC11 and WC10 bits in WSCR2 for the
256-kbyte expansion area, and the WC21 and WC20 bits in WSCR2 for the CP expansion area).
Pin Wait Mode: A specified number of wait states T
T
state and T
state when accessing the external address space always according to the settings of
2
3
the WC1 and WC0 bits (the WC21 and WC20 bits for the CP expansion area). If the
WAIT/CPWAIT pin is low at the falling edge of φ in the last T
inserted. If the WAIT/CPWAIT pin is held low, T
This is useful when inserting four or more T
be inserted for each external device.
Pin Auto-Wait Mode: A specified number of wait states T
between the T
state and T
2
settings of the WC1 and WC0 bits (the WC21 and WC20 bits for the CP expansion area) if the
WAIT/CPWAIT pin is low at the falling edge of φ in the last T
pin is held low, T
states can be inserted only up to the specified number of states.
W
This function enables the low-speed memory interface only by inputting the chip select signal to
the WAIT/CPWAIT pin.
Figure 6.13 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/CPWAIT pin
input disabled.
state when accessing the external address space always according to
3
states, or when changing the number of T
W
state when accessing the external address space according to the
3
can be inserted automatically
W
can be inserted automatically between the
W
or T
state, another T
2
W
states are inserted until it goes high.
W
can be inserted automatically
W
state. Even if the WAIT/CPWAIT
2
Rev. 3.00 Jan 25, 2006 page 133 of 872
Section 6 Bus Controller
state is
W
states to
W
REJ09B0286-0300
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