MPC555
/
MPC556
SYSTEM CONFIGURATION AND PROTECTION
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
6-2
fined by the MPC555 / MPC556 architecture to provide a decrementer interrupt.
This binary counter is clocked by the same frequency as the time base (also de-
fined by the MPC555 / MPC556 architecture). The period for the DEC when driv-
en by a 4-Mhz oscillator is 4295 seconds, which is approximately 71.6 minutes.
•
Real-Time Clock (RTC)
— The RTC is used to provide time-of-day information
to the operating system or application software. It is composed of a 45-bit counter
and an alarm register. A maskable interrupt is generated when the counter reach-
es the value programmed in the alarm register. The RTC is clocked by the same
clock as the PIT.
•
Freeze Support
— The SIU allows control of whether the SWT, PIT, TB, DEC
and RTC should continue to run during the freeze mode.
shows a block diagram of the system configuration and protection logic.
Figure 6-1 System Configuration and Protection Logic
Interrupt
Controller
Bus
Monitor
Periodic Interrupt
Timer
Software
Watchdog Timer
MPC555
Decrementer
MPC555
Time Base Counter
Real-Time
Clock
Clock
TEA
Signal
Interrupt
Interrupt or
System Reset
Interrupt
Interrupt
Module
Configuration
Decrementer
Exception
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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