Clocks and Power Control
MPC885 PowerQUICC Family Reference Manual, Rev. 2
14-14
Freescale Semiconductor
management controllers to continue operating at a fixed frequency, even when the rest of the MPC885 is
operating at a reduced frequency.
SYNCCLK defaults to divout1, where divout1 is equivalent to JDBCK divide by 2, but can be reduced in
frequency by a frequency divider. This frequency divider is controlled by SCCR[DFSYNC].
Figure 14-10. SYNCCLK Divider
The synchronization clock frequency is:
Limitations on SYNCCLK include:
•
SYNCCLK must always have a frequency at least as high as GCLKx.
•
SYNCCLK must and be at least two times the maximum serial clock rate used by the serial ports
in the system.
•
If the time-slot assigner (TSA) is used, SYNCCLK must be at least 2.5 times the maximum serial
clock rate of the TSA.
14.3.2
PIT Clock (PITCLK)
The PIT clock is generated either from EXTCLK or the crystal oscillator circuit (OSCM). This input
source can be divided by either 4 or 512. The PITCLK source and divide factor are selected by
SCCR[PTSEL] and SCCR[PTDIV].
The MODCK[1:2] state at PORESET negation determines the input clock source and prescalar value for
PITCLK. These values can be changed after reset by manipulating the associated bits in the SCCR.
Table 14-5. PITCLK Configuration at PORESET
MODCK [1:2]
PITCLK Prescaler
SCCR[PTDIV]
PITCLK Input Source
SCCR[PTSEL]
00
4
OSCM (crystal oscillator)
01
512
OSCM (crystal oscillator)
10
512
EXTCLK
11
512
EXTCLK
Note:
Since OSCM just uses one frequency input of 10 MHz, it is not possible to get a PITCLK period of 1 second.
This could however be achieved by giving an appropriate input to the EXTCLK.
DFSYNC
CPM
SYNCCLK
divout1
SYNCCLK
freq
divout1
freq
2
2
DFSYNC
×
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Summary of Contents for PowerQUICC MPC870
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Page 1370: ...MPC880 MPC885 PowerQUICC Family Reference Manual Rev 2 E 4 Freescale Semiconductor ...
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