Information

6.2.2.2 Low-voltage detect (LVD)
The chip includes a system for managing low voltage conditions to protect memory
contents and control MCU system states during supply voltage variations. The system
consists of a power-on reset (POR) circuit and an LVD circuit with a user-selectable trip
voltage. The LVD system is always enabled in normal run, wait, or stop mode. The LVD
system is disabled when entering VLPx, LLS, or VLLSx modes.
The LVD can be configured to generate a reset upon detection of a low voltage condition
by setting the PMC's LVDSC1[LVDRE] bit to 1. The low voltage detection threshold is
determined by the PMC's LVDSC1[LVDV] field. After an LVD reset has occurred, the
LVD system holds the MCU in reset until the supply voltage has risen above the low
voltage detection threshold. The RCM's SRS0[LVD] bit is set following either an LVD
reset or POR.
6.2.2.3 Computer operating properly (COP) watchdog timer
The computer operating properly (COP) watchdog timer (WDOG) monitors the operation
of the system by expecting periodic communication from the software. This
communication is generally known as servicing (or refreshing) the COP watchdog. If this
periodic refreshing does not occur, the watchdog issues a system reset. The COP reset
causes the RCM's SRS0[WDOG] bit to set.
6.2.2.4 Low leakage wakeup (LLWU)
The LLWU module provides the means for a number of external pins, the RESET pin,
and a number of internal peripherals to wake the MCU from low leakage power modes.
The LLWU module is functional only in low leakage power modes.
• In LLS mode, only the RESET pin via the LLWU can generate a system reset.
• In VLLSx modes, all enabled inputs to the LLWU can generate a system reset.
After a system reset, the LLWU retains the flags indicating the input source of the last
wakeup until the user clears them.
NOTE
Some flags are cleared in the LLWU and some flags are
required to be cleared in the peripheral module. Refer to the
individual peripheral chapters for more information.
Reset
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
156 Freescale Semiconductor, Inc.