Datasheet

Section 6 Bus Controller (BSC)
Rev. 3.00 Mar 17, 2006 page 181 of 926
REJ09B0283-0300
6.6.9 Wait Control
There are two ways of inserting wait states in a DRAM access cycle: program wait insertion and
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
c1
state and T
c2
state, according to the settings in registers WTCRA and WTCRB.
Pin Wait Insertion: When the WAITE bit in BCR 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 state, a
program wait (T
w
) is first inserted. If the WAIT pin is low at the falling edge of φ in the last T
c1
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.
Figures 6.26 and 6.27 show examples of wait cycle insertion timing in the case of 2-state and 3-
state column address output cycles.