Datasheet

56F8346 Technical Data, Rev. 15
148 Freescale Semiconductor
Preliminary
and DCAEO are used to make this duty cycle adjustment where needed.
DCAOE and DCAEO are calculated as follows:
The timing of write cycles is different when WWS = 0 than when WWS > 0. Therefore, some parameters
contain two sets of numbers to account for this difference. Use the “Wait States Configuration” column of
Table 10-16 to make the appropriate selection.
Figure 10-4 External Memory Interface Timing
Note: When multiple lines are given for the same wait state configuration, calculate each and then select the
smallest or most negative.
DCAOE =
=
0.5 - MAX XTAL duty cycle, if ZSRC selects prescaler clock and the prescaler is set to ÷ 1
0.0 all other cases
DCAEO =
=
MIN XTAL duty cycle - 0.5, if ZSRC selects prescaler clock and the prescaler is set to
÷ 1
0.0 all other cases
Example of DCAOE and DCAEO calculation
Assuming prescaler is set for
÷ 1 and prescaler clock is selected by ZSRC, if XTAL duty cycle
ranges between 45% and 60% high:
DCAOE = .50 - .60 = - 0.1
DCAEO = .45 - .50 = - 0.05
t
DRD
t
RDD
t
AD
t
DOH
t
DOS
t
DWR
t
RDWR
t
WAC
t
WRRD
t
WR
t
AWR
t
WRWR
t
ARDD
t
RDA
t
RDRD
t
RD
t
ARDA
Data Out Data In
A0-Axx,CS
RD
WR
D0-D15
Note: During read-modify-write instructions and internal instructions, the address lines do not change state.