ST7L15 datasheet(24/138 Pages) STMICROELECTRONICS

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ST7L15, ST7L19

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SUPPLY, RESET AND CLOCK MANAGEMENT (cont’d)

7.4 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):

■ An external source

■ Crystal or ceramic resonator oscillators

■ An internal high frequency RC oscillator

The

associated

hardware

configurations

are

shown in Table 4. Refer to Section 13 ELECTRI-

CAL CHARACTERISTICS for more details.

7.4.1 External Clock Source

In external clock mode, a clock signal (square, si-

nus or triangle) with ~50% duty cycle must 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 the external clock.

7.4.2 Crystal/Ceramic Oscillators

In this mode, with a self-controlled gain feature, an

oscillator of any frequency from 1 to 16 MHz can

be placed on OSC1 and OSC2 pins. This family of

oscillators has the advantage of producing a very

accurate rate on the main clock of the ST7. In this

mode of the multi-oscillator, the resonator and the

load capacitors must be placed as close as possi-

ble to the oscillator pins to minimize output distor-

tion and start-up stabilization time. The loading ca-

pacitance 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.

7.4.3 Internal RC Oscillator

In this mode, the tunable 1% RC oscillator is the

main clock source. The two oscillator pins must be

tied to ground if dedicated to oscillator use, other-

wise they are general purpose I/O.

The calibration is done through the RCCR[7:0] and

SICSR[6:5] registers.

Table 4. ST7 Clock Sources

Hardware Configuration

OSC1

OSC2

EXTERNAL

ST7

SOURCE

OSC1

OSC2

LOAD

CAPACITORS

ST7

CL2

CL1

OSC1

OSC2

ST7

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