Freescale Semiconductor MPC5604B, Quick Start Manual

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4. RTC/API: Real Time Clock/ Autonomous Periodic Interrupt
Figure 40 : RTC/API Architecture (R.M. Rev8 – Fig. 13-1)
The Real Time Clock is an independent 32-bit timer, clocked by either internal RC oscillators
(128kHz or 16MHz) or by a slow external crystal (32kHz). By using dividers by 32 and/or 512,
we can count in
resolutions of a few µs or a few ms up to thousands of seconds (see the last table
of this section). RTC module has a 12-bit match value, that is compared to the bits [21:10] of the
counter, and it can trigger a wakeup or interrupt event.
The Autonomous Periodic Interrupt (API) module can trigger wakeup or interrupt events
periodically; a 10-bit period value is added to the bits [22:31] of current value of the counter,
giving an offset match register that can generate a trigger. Once an event is triggered, the offset
register is updated with a new match value, therefore resulting in periodically triggered events.
The RTC Supervisor Control (RTCSUPV) register can only be modified in device modes and its
SUPV bit can limit access to other registers (true by default) or not. Writing ‘0’ to this bit will
grant access to other registers in user modes.
Figure 41 : RTC Control Register (R.M. Rev8 – Fig. 13-2)