Input Clocks
4
4.1
Input Clocks
System Clock Timing
Table 5. SYSCLK AC Timing Specifications
This section discusses the timing for the input clocks.
provides the system clock (SYSCLK) AC timing specifications for the MPC8548E.
At recommended operating conditions (see
with OV
DD
= 3.3 V ± 165 mV
.
Parameter/Condition
SYSCLK frequency
SYSCLK cycle time
SYSCLK rise and fall time
SYSCLK duty cycle
SYSCLK jitter
Symbol
f
SYSCLK
t
SYSCLK
t
KH
, t
KL
t
KHK
/t
SYSCLK
—
Min
16
7.5
0.6
40
—
Typ
—
—
1.0
—
—
Max
133
60
1.2
60
± 150
Unit
MHz
ns
ns
%
ps
Notes
1, 6, 7, 8
6, 7, 8
2
3
4, 5
Notes:
1.
Caution:
The CCB clock to SYSCLK ratio and e500 core to CCB clock ratio settings must be chosen such that the resulting
SYSCLK frequency, e500 (core) frequency, and CCB clock frequency do not exceed their respective maximum or minimum
operating frequencies.Refer to
and
for ratio
settings.
2. Rise and fall times for SYSCLK are measured at 0.6 and 2.7 V.
3. Timing is guaranteed by design and characterization.
4. This represents the total input jitter—short term and long term—and is guaranteed by design.
5. The SYSCLK driver’s closed loop jitter bandwidth should be <500 kHz at –20 dB. The bandwidth must be set low to allow
cascade-connected PLL-based devices to track SYSCLK drivers with the specified jitter.
6. This parameter has been adjusted slower according to the workaround for device erratum GEN 13.
7. For spread spectrum clocking. Guidelines are + 0% to –1% down spread at modulation rate between 20 and 60 kHz on
SYSCLK.
8. System with operating core frequency less than 1200 MHz must limit SYSCLK frequency to 100 MHz maximum..
4.2
Real Time Clock Timing
The RTC input is sampled by the platform clock (CCB clock). The output of the sampling latch is then
used as an input to the counters of the PIC and the TimeBase unit of the e500. There is no jitter
specification. The minimum pulse width of the RTC signal should be greater than 2x the period of the CCB
clock. That is, minimum clock high time is 2
×
t
CCB
, and minimum clock low time is 2
×
t
CCB
. There is
no minimum RTC frequency; RTC may be grounded if not needed.
MPC8548E PowerQUICC™ III Integrated Processor Hardware Specifications, Rev. 6
Freescale Semiconductor
15
FREESCALE [ FREESCALE SEMICONDUCTOR, INC ]
