Motorola MPC823e Reference Manual page 273

• Software Watchdog Timer —Asserts a reset or nonmaskable interrupt that is selected
by the system protection control register (SYPCR) if the software fails to service the
software watchdog timer after a certain period of time. After system reset, the software
watchdog timer, if enabled, selects a maximum timeout period and asserts a system
reset if the timeout is reached. The software watchdog timer can be disabled or its
timeout period can be changed in the SYPCR. Once the SYPCR is written, it cannot be
written again until a system reset.
• Periodic Interrupt Timer —Generates periodic interrupts to be used with the real-time
operating system or the application software. The periodic interrupt timer is clocked by
the PITRTCLK clock, thus providing a period from 122 microseconds to 8,000
milliseconds assuming a 32.768kHz crystal. The periodic interrupt timer function can be
disabled if it is not needed.
• PowerPC Timebase Counter —Provides a timebase reference for the operating
system or application software. This 64-bit timebase counter is defined by the PowerPC
architecture and has two independent reference registers that generate a maskable
interrupt when the programmed value in one of the registers is reached. The associated
bit in the timebase status register is set for the reference register that generated the
interrupt. The timebase is clocked by the TMBCLK clock.
• PowerPC Decrementer —Provides a decrementer interrupt and is clocked at the same
frequency as the timebase. This 32-bit decrementing counter is defined by the
PowerPC architecture to be clocked by the TMBCLK clock. When it is driven by a 4MHz
oscillator the period for the decrementer is 4,295 seconds, which is approximately 71.6
minutes.
• Real-Time Clock —Provides a 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 (RTCAL) register. The real-time clock is clocked by the PITRTCLK clock.
• Freeze Support —The system interface unit determines whether the software
watchdog timer, periodic interrupt timer, timebase, decrementer, and real-time clock will
continue to run in freeze mode.
MOTOROLA MPC823e REFERENCE MANUAL
System Interface Unit
12-3