Motorola MPC533 Reference Manual page 235

6.1.8 Real-Time Clock (RTC)
The RTC is a 32-bit counter and pre-divider used to provide a time-of-day indication to the
operating system and application software as show in Figure 6-7. It is clocked by the
PITRTCLK clock. The counter is not affected by reset and operates in all low-power
modes. It is initialized by software. The RTC can be programmed to generate a maskable
interrupt when the time value matches the value programmed in its associated alarm
register. It can also be programmed to generate an interrupt once a second. A control and
status register is used to enable or disable the different functions and to report the interrupt
source.
PITRTCLK can be divided by 4 or 256. See Table 8-1 for
default settings.
FREEZE
Clock
PITRTCLK
Disable
Clock
6.1.9 Periodic Interrupt Timer (PIT)
The periodic interrupt timer consists of a 16-bit counter clocked by the PITRTCLK clock
signal supplied by the clock module as shown in Figure 6-8.
The 16-bit counter counts down to zero when loaded with a value from the PITC register.
After the timer reaches zero, the PS bit is set and an interrupt is generated if the PIE bit is
a logic one. The software service routine should read the PS bit and then write a zero to
terminate the interrupt request. At the next input clock edge, the value in the PITC is loaded
into the counter, and the process starts over again.
When a new value is written into the PITC, the periodic timer is updated, the divider is
reset, and the counter begins counting. If the PS bit is not cleared, an interrupt request is
MOTOROLA
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
NOTE
RTSEC
Divide
By 15625
Divide
By 78125
4-MHz/20-MHz crystal
Figure 6-7. RTC Block Diagram
Chapter 6. System Configuration and Protection
System Configuration and Protection Features
MUX
32-bit Counter (RTC)
=
32-bit Register (RTCAL)
Sec
Interrupt
Alarm
Interrupt
6-21