MPC555
/
MPC556
CLOCKS AND POWER CONTROL
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
8-7
8.6 MPC555
/
MPC556 Internal Clock Signals
The internal clocks generated by the clocks module are shown in
. The
clocks module also generates the CLKOUT and ENGCLK external clock signals. The
PLL synchronizes these signals to each other. The PITRTCLK frequency and source
are specified by the RTDIV and RTSEL bits in the SCCR. When the backup clock is
functioning as the system clock, the backup clock is automatically selected as the time
base clock source and is twice the MPC555 / MPC556 system clock.
Figure 8-4 MPC555 / MPC556 Clocks
Note that GCLK1_50, GCLK2_50, and CLKOUT can have a lower frequency than
GCLK1 and GCLK2. This is to enable the external bus operation at lower frequencies
(controlled by EBDF in the SCCR). GCLK2_50 always rises simultaneously with
GCLK1
GCLK2
GCLK1_50
GCLK2_50
CLKOUT
T1
T2
T3
T4
GCLK1_50
GCLK2_50
(EBDF = 00)
(EBDF = 00)
(EBDF = 01)
(EBDF = 01)
CLKOUT
(EBDF = 00)
(EBDF = 01)
System Clock
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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