User's Manual

UMXXX
does exploit the embedded digital filter of the ADC peripheral for PDM to PCM
conversion when reading the PDM output of the MEMS microphone MP34DT05-A.
The low-speed clock is used in low-power mode and can be supplied by the internal RC
oscillator or by an external crystal (32kHz +/-50ppm). The high-speed clock is supplied by
a fast-starting internal RC oscillator (16MHz) while the external crystal is starting up. The
high-speed external crystal (16 or 32MHz) is strictly required to enable the BLE radio.
In order to support the highest computational load, the 32MHz XO must be used. When
32MHz XO is used, the Cortex-M0, the DMA and the APB tree run at 32MHz while the rest
of the clock tree runs at 16MHz. When 16MHz XO is used, the Cortex-M0 and all the clock
tree runs at 16MHz.
BlueNRG-2 states
• Preactive (reachable from Reset, Standby or Sleep, goes to Active): after power-
on-reset, all digital power supplies are stable; internal 16MHz and 32kHz RC
oscillators are used.
• Active (reachable only from Preactive): the external high-frequency crystal is used
(16MHz +/-50ppm or 32MHz) to enable BLE communication; the internal 16MHz
RC oscillator is switched off; the higher the accuracy of the crystal, the lower the
power consumption is; the BlueNRG-2 sensor node uses a 32MHz +/-10ppm
crystal. In active mode the radio can be activated for transmission (TX) or reception
(RX). This is the state used by BlueNRG-2 when the user application is
running or there is a BLE event to serve.
• Standby (reachable from Active, can go to Preactive): RAM retention is used (12 or
24kB); 5 different GPIOs can be used to wake-up (IO9, IO10, IO11 which have an
internal pull-up, and IO12, IO13 which require an external drive); the BlueNRG-2
sensor node uses IO11 connected to the user button, IO12 connected to the
interrupt pin of LIS2MDL magnetometer, and IO13 connected to the interrupt pin of
of LSM6DSO accelerometer and gyroscope. The wake-up time is typically 200us.
• Sleep (reachable from Active, can go to Preactive): RAM retention is used (12 or
24kB); the low-frequency oscillator is switched on to serve periodic BLE connection
events; as in Standby state, 5 different GPIOs can also be used to wake-up. This
is the state used by the BlueNRG-2 tile to save power when the user
application is not running and the device is waiting for a BLE event to serve.
BLE FIRMWARE STACK AND MEMORY MAP
Program memory, data memory, registers and I/O ports are organized in a linear 32-bit
address space.