Datasheet
56F8366 Technical Data, Rev. 7
154 Freescale Semiconductor
Preliminary
10.8 External Memory Interface Timing
The External Memory Interface is designed to access static memory and peripheral devices. Figure 10-5
shows sample timing and parameters that are detailed in Table 10-16.
The timing of each parameter consists of both a fixed delay portion and a clock related portion, as well as
user controlled wait states. The equation:
t = D + P * (M + W)
should be used to determine the actual time of each parameter. The terms in this equation are defined as:
When using the XTAL clock input directly as the chip clock without prescaling (ZSRC selects prescaler
clock and prescaler is set to
÷
1),
the EMI quadrature clock is generated using both edges of the EXTAL
clock input. In this situation only, parameter values must be adjusted for the duty cycle at XTAL. DCAOE
and DCAEO are used to make this duty cycle adjustment where needed.
DCAOE and DCAEO are calculated as follows:
Bias Current, low-drive mode I
BIASL
—80110μA
Quiescent Current, power-down mode I
PD
—0 1μA
t = Parameter delay time
D = Fixed portion of the delay, due to on-chip path delays
P = Period of the system clock, which determines the execution rate of the part
(i.e., when the device is operating at 60MHz, P = 16.67 ns)
M = Fixed portion of a clock period inherent in the design; this number is adjusted to account
for possible derating of clock duty cycle
W = Sum of the applicable wait state controls. The “Wait State Controls” column of
Table 10-16
shows the applicable controls for each parameter and the EMI chapter of the
56F8300 Peripheral User Manual
details what each wait state field controls.
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
Table 10-15 Crystal Oscillator Parameters
Characteristic Symbol Min Typ Max Unit