ST7DALIF2 datasheet(36/171 Pages) STMICROELECTRONICS

36 / 171 page

Supply, reset and clock management

ST7DALIF2

36/171

9.5

Multi-oscillator (MO)

The main clock of the ST7 can be generated by four different source types coming from the

multi-oscillator block (1 to 16 MHz or 32 kHz):

●

an external source

●

5 crystal or ceramic resonator oscillators

●

an internal high frequency RC oscillator

Each oscillator is optimized for a given frequency range in terms of consumption and is

selectable through the option byte. The associated hardware configurations are shown in

Table 10. Refer to the electrical characteristics section for more details.

External clock source

In this external clock mode, a clock signal (square, sinus or triangle) with ~50% duty cycle

has to drive the OSC1 pin while the OSC2 pin is tied to ground.

Note:

When the Multi-Oscillator is not used, PB4 is selected by default as external clock.

Crystal/ceramic oscillators

This family of oscillators has the advantage of producing a very accurate rate on the main

clock of the ST7. The selection within a list of 4 oscillators with different frequency ranges

has to be done by option byte in order to reduce consumption (refer to Section 22.1 on page

161 for more details on the frequency ranges). In this mode of the multi-oscillator, the

resonator and the load capacitors have to be placed as close as possible to the oscillator

pins in order to minimize output distortion and start-up stabilization time. The loading

capacitance values must be adjusted according to the selected oscillator.

These oscillators are not stopped during the RESET phase to avoid losing time in the

oscillator start-up phase.

Internal RC oscillator

In this mode, the tunable 1%RC oscillator is used as main clock source. The two oscillator

pins have to be tied to ground.

ST7DALIF2 Datasheet(PDF) 36 Page - STMicroelectronics