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MPC555
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MPC556
SYSTEM CONFIGURATION AND PROTECTION
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
6-18
Figure 6-9 SWT Block Diagram
6.11 Freeze Operation
When the FREEZE line is asserted, the clocks to the software watchdog, the periodic
interrupt timer, the real-time clock, the time base counter, and the decrementer can be
disabled. This is controlled by the associated bits in the control register of each timer.
If programmed to stop during FREEZE assertion, the counters maintain their values
while FREEZE is asserted, unless changed by the software. The bus monitor, howev-
er, remains enabled regardless of this signal.
6.12 Low Power Stop Operation
When the processor is set in a low-power mode (doze, sleep, or deep sleep), the soft-
ware watchdog timer is frozen. It remains frozen and maintain its count value until the
processor exits this state and resumes executing instructions.
The periodic interrupt timer, decrementer, and time base are not affected by these low-
power modes. They continue to run at their respective frequencies. These timers are
capable of generating an interrupt to bring the MCU out of these low-power modes.
6.13 System Configuration and Protection Registers
This section provides diagrams and bit descriptions of the system configuration and
protection registers.
Disable
Clock
FREEZE
SWR / Decrementer
Time-out
16-bit
SWTC
SWE
Service
Logic
Reload
Rollover = 0
Reset
SWSR
MUX
2048
System
SWP
Clock
Divide By
or
NMI
(SYPCR)
(SYPCR)
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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