JN516X Datasheet, PDF (58/94 Pages) NXP Semiconductors – IEEE802.15.4 Wireless Microcontroller

When entering into sleep mode, there is an option to retain the RAM contents throughout the sleep period. If the
wakeup timers are not to be used for a wakeup event and the application does not require them to run continually,
then power can be saved by switching off the 32kHz oscillator if selected as the 32kHz system clock through software
control. The oscillator will be restarted when a wakeup event occurs.
Whilst in sleep mode one of four possible events can cause a wakeup to occur: transitions on DIO inputs, expiry of
wakeup timers, pulse counters maturing or comparator events. If any of these events occur, and the relevant
interrupt is enabled, then an interrupt is generated that will cause a wakeup from sleep. It is possible for multiple
wakeup sources to trigger an event at the same instant and only one of them will be accountable for the wakeup
period. It is therefore necessary in software to remove all other pending wakeup events prior to requesting entry back
into sleep mode; otherwise, the device will re-awaken immediately.
When wakeup occurs, a similar sequence of events to the reset process described in Section 6.1 happens, including
the checking of the supply voltage by the Supply Voltage Monitor 6.4. The High-Speed RC oscillator is started up,
once stable the power to CPU system is enabled and the reset is removed. Software determines that this is a reset
from sleep and so commences with the wakeup process. If RAM contents were held through sleep, wakeup is quicker
as the software does not have to initialise RAM contents meaning the application can recommence more quickly. See
Section 19.3.4 for wake-up timings.
18.3.1 Wakeup Timer Event
The JN516X contains two 41-bit wakeup timers that are counters clocked from the 32kHz oscillator, and can be
programmed to generate a wake-up event. Following a wakeup event, the timers continue to run. These timers are
described in Section 11.3.
Timer events can be generated from both of the two timers; one is intended for use by the 802.15.4 protocol, the
other being available for use by the Application running on the CPU. These timers are available to run at any time,
even during sleep mode.
18.3.2 DIO Event
Any DIO pin when used as an input has the capability, by detecting a transition, to generate a wake-up event. Once
this feature has been enabled the type of transition can be specified (rising or falling edge). Even when groups of
DIO lines are configured as alternative functions such as the UARTs or Timers etc, any input line in the group can still
be used to provide a wakeup event. This means that an external device communicating over the UART can wakeup
a sleeping device by asserting its RTS signal pin (which is the CTS input of the JN516X).
18.3.3 Comparator Event
The comparator can generate a wakeup interrupt when a change in the relative levels of the positive and negative
inputs occurs. The ability to wakeup when continuously monitoring analogue signals is useful in ultra-low power
applications. For example, the JN516x can remain in sleep mode until the voltage drops below a threshold and then
be woken up to deal with the alarm condition and the comparator has a low current mode to facilitate this.
18.3.4 Pulse Counter
The JN516x contains two 16 bit pulse counters that can be programmed to generate a wake-up event. Following the
wakeup event the counters will continue to operate and therefore no pulse will be missed during the wake-up
process. These counters are described in Section 12.To minimize sleep current it is possible to disable the 32K RC
oscillator and still use the pulse counters to cause a wake-up event, provided debounce mode is not required.
18.4 Deep Sleep Mode
Deep sleep mode gives the lowest power consumption. All switchable power domains are off and most functions in
the VDD supply power domain are stopped, including the 32kHz RC oscillator. However, the Brown-Out Reset
remains active as well as all the DIO cells. This mode can be exited by a hardware reset on the RESETN pin, or an
enabled DIO or comparator wakeup event. In all cases, the wakeup sequence is equivalent to a power-up sequence,
with no knowledge retained from the previous time the device was awake.
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JN-DS-JN516x v1.1 Production
© NXP Laboratories UK 2013