PMU & PLL
7-7
GMS30C7201 Data Sheet
Wake-up Debounce and Interrupt
The Wake-up events are debounced as follows:
Each of the event signals which are liable to noise (
nRESET
,
RTC
,
nPMWAKEUP
, and
Modem Ring Indicator
,
Power Adapter Condition
) is re-timed to a 250Hz clock
derived from the low power (4kHz) clock. After filtering to a quarter of 250 Hz, each
event has an associated
‘
sticky
’
register bit.
nPMWAKEUP
is an external input, which
may be typically connected to an
“
ON
”
key.
A
‘
sticky
’
bit is a register bit that is set by the incoming event, but is only reset by the
CPU. Thus should a PLL drop out of lock momentarily (for example) the CPU will be
informed of the event, even if the PLL has regained lock by the time the CPU can read
its associated register bit.
The
nPMWAKEUP
, Modem, Real Time Clock and Power Adapter condition inputs are
combined to form the PMU Interrupt. Each of these three interrupt sources may be
individually enabled.
To make use of the
nPMWAKEUP
Interrupt, (for example) controlling software will
need to complete the following tasks:
Enable the
nPMWAKEUP
interrupt bit, by writing 0 to bit 9 of the ResetStatus
register.
Once an interrupt has occurred, read the RESET / Status register to identify
the source(s) of interrupt. In the case of a
nPMWAKEUP
event, the register
will return 0x10.
Clear the appropriate
‘
sticky
’
bit by writing a 1 to the appropriate location (in the
nPMWAKEUP
case, this will be 0x10.).
PORTA Wake-up Sequence
The PORTA interrupt is OR gated with
nPMWAKEUP
to support additional wake up
sources.
Each PORTA input signal can be used as a wake up source, they are enabled using the
Interrupt MASK Register. After wake up, s/w should program the PORTA Interrupt
MASK Register and/or the PMU ResetStatus Register.
One possible application is to use the
nDCD
signal, from the a UART interface, as a
wake up source, by connecting
nDCD
to a PORTA input. In Deep Sleep mode,
nDCD
can wake up the system by generating a PORTA interrupt request to the PMU block.
The PMU state machine then returns the system to the operational mode.