NINA-B50 series - Hardware integration manual
UBX-22021116 - R02
Module integration
Page 13 of 57
C1-Public
2.2.3
Real Time Clock (RTC)
NINA-B50 series modules use a 32.768 kHz low power clock to enable different sleep modes.
The Real Time Clock (RTC) can be generated from either of the following sources:
•
Internal 32 kHz FRO
•
External crystal or clock source
You can source the clock from an external 32 kHz Crystal Oscillator (OSC) or from the embedded
32 kHz Free Running Oscillator (FRO) on . The RTC block includes an internal clock validation
mechanism to verify the stability of the clock from OSC. also features a clock switch that enables the
module to transition from the 32 kHz FRO to OSC when the OSC clock is stable. If the software
disables the 32 kHz OSC, the module can revert to the 32 kHz FRO clock.
To achieve the lowest sleep current consumption in the module, use an external crystal or external
clock source. Although the 32 kHz FRO consumes slightly more sleep current, it provides a leaner
BOM.
The RTC functions in all low power modes and can generate an interrupt to exit any low power mode.
See also
. The module operates in one of two modes:
•
Power-on mode:
RTC remains powered during module power-up and all RTC registers are
accessible by software and all functions are operational. If enabled, the 32.768 kHz clock can be
supplied to the rest of the module.
•
Power-down mode:
During module power-down, RTC is powered and is electrically isolated from
the rest of the chip but continues to increment the time counter (if enabled) and retain the state
of the RTC registers. The RTC registers are not accessible. The time counter can generate multiple
interrupts and events to the CPU and radio as well as internal and external hardware blocks. The
frequency of the interrupt is 1 Hz by default but can also be configured to trigger every 2, 4, 8, 16,
32, 64, or 128 Hz.
☞
For RTC pinout information, see also NINA-B50 data sheet
2.2.3.1
32 kHz FRO
–
Internal oscillator
Sourcing the module clock from the embedded 32 kHz FRO can lead to a slight increase in power
consumption. However, this choice of oscillator offers a more cost-effective BOM that reduces the
cost to end users.
If the module clock is sourced from the FRO, pins
EXTAL32K
and
XTAL32K
can be reassigned as
GPIOs.
The 32 kHz FRO is enabled after Power-On-Reset (POR) and can be disabled by software only if
external crystal is connected. For more information, see also NINA-B50 data sheet
2.2.3.2
External crystal
NINA-B50 series modules NINA-B50 supports two input pins for connecting an optional external low-
frequency crystal (LFXO) as the RTC source. In this configuration, the module operates with the
lowest overall power consumption. The specification for the optional low-frequency crystal is available
in the NINA-B50 series data sheet
describes the specification of the crystal used on EVK-NINA-B506. Note that the 32 kHz
crystal is not mounted on EVK-NINA-B501.
Table 2: Specification of the low-frequency crystal used on the NINA-B506 EVK evaluation kit
Component
Value
Note
Crystal
32.768 kHz
–
20 ppm
EPSON FC-12M used on NINA-B50 EVK
