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4.5.10
Wait Control
There are two ways of inserting wait states in a DRAM access cycle: (1) program wait insertion
and (2) pin wait insertion using the WAIT pin.
Wait states are inserted to extend the CAS assertion period in a read access to DRAM space, and
to extend the write data setup time relative to the falling edge of CAS in a write access.
Program Wait Insertion: When the bit in ASTCR corresponding to an area designated as DRAM
space is set to 1, from 0 to 7 wait states can be inserted automatically between the T
state and T
c1
c2
state, according to the settings in registers WTCRA and WTCRB.
Pin Wait Insertion: When the WAITE bit in the BCR register is set to 1 and the ASTCR bit is set
to 1, wait input by means of the WAIT pin is enabled. When DRAM space is accessed in this
) is first inserted. If the WAIT pin is low at the falling edge of ø in the
state, a program wait (T
w
state is inserted. If the WAIT pin is held low, T
last T
or T
state, another T
states are inserted
c1
w
w
w
until it goes high.
Figures 4.25 and 4.26 show examples of wait state insertion timing in the case of 2-state and 3-
state column address output cycles.
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