Motorola MPC533 Reference Manual page 216

reference for the operating system or application software. The TB has four
independent reference registers that can generate a maskable interrupt when the
time-base counter reaches the value programmed in one of the four reference
registers. The associated bit in the TB status register will be set for the reference
register which generated the interrupt.
• Real-Time Clock (Section 6.1.8, "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 reaches the value programmed in the alarm register. The
RTC is clocked by the same clock as the PIT.
• Periodic Interrupt Timer (Section 6.1.9, "Periodic Interrupt Timer (PIT)")—The
SIU provides a timer to generate periodic interrupts for use with a real-time
operating system or the application software. The PIT provides a period from 1 µs
to 4 seconds with a four-MHz crystal or 200 ns to 0.8 ms with a 20-MHz crystal. The
PIT function can be disabled.
• Software Watchdog Timer (Section 6.1.10, "Software Watchdog Timer
(SWT)")—The SWT asserts a reset or non-maskable interrupt, as selected by the
system protection control register (SYPCR), if the software fails to service the SWT
for a designated period of time (e.g., because the software is trapped in a loop or
lost). After a system reset, this function is enabled with a maximum time-out period
and asserts a system reset if the time-out is reached. The SWT can be disabled or its
time-out period can be changed in the SYPCR. Once the SYPCR is written, it cannot
be written again until a system reset.
• Freeze Support (Section 6.1.11, "Freeze Operation")—The SIU allows control of
whether the SWT, PIT, TB, DEC, and RTC should continue to run during the freeze
mode.
• Low Power Stop (Section 6.1.12, "Low Power Stop Operation")—In low power
modes, specific timers are frozen but others are not.
Figure 6-1 shows a block diagram of the system configuration and protection logic.
6-2
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
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