Clocks and Power Control
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
14-13
14.3.1.3
CLKOUT Special Considerations: 1:2:1 Mode
To enable synchronization of a system to the EXTCLK signal while still allowing the internal circuits of
the MPC885 to operate at an increased frequency, it is necessary to maintain synchronization of the
EXTCLK and CLKOUT signal. Specifically, this operation entails:
•
input clock source EXTCLK
•
internal clock of 2xEXTCLK, provided by multiplying EXTCLK by 2 in the DPLL (by
programming PLPRCR[MFI]=10, PLPRCR[MFN]=0, PLPRCR [MFD]=0, PLPRCR[PDF]=4,
PLPRCR[S]=0)
•
external bus clock CLKOUT with frequency equivalent to EXTCLK, provided by dividing
GCLK2 by 2 (by programming SCCR[EBDF]=01)
This is also known as 1:2:1 mode. In this mode, in order to allow multiple devices clocked by the same
EXTCLK source to maintain synchronization on the external bus, EXTCLK and CLKOUT must be in
phase. This operation can be guaranteed, but it requires that SCCR[EBDF] be written first, followed by
the write to PLPRCR[MFI, MFN, MFD]. Synchronization between EXTCLK and CLKOUT is only
possible when the total multiplication factor between EXTCLK and CLKOUT is maintained as an integer
number.
14.3.1.4
Baud Rate Generator Clock (BRGCLK)
The baud rate generator clock (BRGCLK) is used by the four baud rate generators of the communication
processor module and by the memory controller refresh counter. The baud rate generator clock is
controlled independently in order to allow the baud rate generators and memory refresh rate to continue
operating at a fixed frequency, even when the rest of the MPC885 is operating at a reduced frequency.
BRGCLK 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[DFBRG].
Figure 14-9. BRGCLK Divider
The baud rate generator clock frequency is:
14.3.1.5
Synchronization Clock (SYNCCLK, SYNCCLKS)
The synchronization clock signals (SYNCCLK and SYNCCLKS, collectively as SYNCCLK) are used by
the signal synchronization circuitry in the serial ports of the communication processor module. The signal
synchronization circuitry is used to sample and synchronize asynchronous external signals provided to
these ports. SYNCCLK allows the serial interface, serial communication controller, and serial
DFBRG
CPM and
UPM
(Refresh
BRGCLK
divout1
Timer)
BRGCLK
freq
divout1
freq
2
2
DFBRG
×
(
)
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=
Summary of Contents for PowerQUICC MPC870
Page 98: ...MPC885 PowerQUICC Family Reference Manual Rev 2 I 4 Freescale Semiconductor ...
Page 118: ...MPC885 Overview MPC885 PowerQUICC Family Reference Manual Rev 2 1 20 Freescale Semiconductor ...
Page 158: ...The MPC8xx Core MPC885 PowerQUICC Family Reference Manual Rev 2 3 18 Freescale Semiconductor ...
Page 288: ...MPC885 PowerQUICC Family Reference Manual Rev 2 III 4 Freescale Semiconductor ...
Page 554: ...MPC885 PowerQUICC Family Reference Manual Rev 2 V 6 Freescale Semiconductor ...
Page 1090: ...UTOPIA Interface MPC885 PowerQUICC Family Reference Manual Rev 2 43 8 Freescale Semiconductor ...
Page 1312: ...Byte Ordering MPC885 PowerQUICC Family Reference Manual Rev 2 A 8 Freescale Semiconductor ...
Page 1336: ...MPC885 PowerQUICC Family Reference Manual Rev 2 D 16 Freescale Semiconductor ...
Page 1358: ...MPC885 PowerQUICC Family Reference Manual Rev 2 D 38 Freescale Semiconductor ...
Page 1370: ...MPC880 MPC885 PowerQUICC Family Reference Manual Rev 2 E 4 Freescale Semiconductor ...
Page 1386: ...Revision History MPC885 PowerQUICC Family Reference Manual Rev 2 I 2 Freescale Semiconductor ...