A. IDLE instruction is executed to put the device
into HALT mode.
B. The LPM block responds to the HALT signal, SYSCLK
is held for a maximum 16 INTOSC1 clock cycles
before being turned off. This delay enables the
CPU pipeline and any other pending operations to
flush properly.
C. Clocks to the peripherals are turned off and the PLL is shut down. If a quartz
crystal or ceramic resonator is used as the clock source, the internal
oscillator is shut down as well. The device is now in HALT mode and consumes
very little power. It is possible to keep the internal
oscillators (INTOSC1 and INTOSC2) and the watchdog alive in HALT MODE. This is
done by writing 1 to CLKSRCCTL1.WDHALTI. After the IDLE instruction is executed,
a delay of five OSCCLK cycles (minimum) is needed before the wake-up signal
could be asserted.
D. When the GPIOn pin (used to bring the device out
of HALT) is driven low, the oscillator is turned
on and the oscillator wake-up sequence is
initiated. The GPIO pin should be driven high only
after the oscillator has stabilized. This enables
the provision of a clean clock signal during the
PLL lock sequence. Because the falling edge of the
GPIO pin asynchronously begins the wake-up
procedure, care should be taken to maintain a low
noise environment before entering and during HALT
mode.
E. The wake-up signal fed to a GPIO pin to wake up
the device must meet the minimum pulse width
requirement. Furthermore, this signal must be free
of glitches. If a noisy signal is fed to a GPIO
pin, the wake-up behavior of the device will not
be deterministic and the device may not exit
low-power mode for subsequent wake-up
pulses.
F. When CLKIN to the core is enabled, the device
will respond to the interrupt (if enabled), after
some latency. The HALT mode is now exited.
G. Normal operation resumes.
H. The user must relock the PLL upon HALT wakeup to
ensure a stable PLL lock.