ST72334J datasheet(30/125 Pages) STMICROELECTRONICS

30 / 125 page

ST72334J/N, ST72314J/N, ST72124J

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MULTI-OSCILLATOR (MO)

The main clock of the ST7 can be generated by 7

different sources coming from the multi-oscillator

block:

an external source

4 crystal or ceramic resonator oscillators

1 external RC oscillator

1 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.

External Clock Source

The default OPTION BYTE value selects the Ex-

ternal Clock in the MO block. In this 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 (see Figure 19).

Figure 19. MO External Clock

Crystal/Ceramic Oscillators

This family of oscillators has the advantage of pro-

ducing a high accuracy on the main clock of the

ST7. The selection within a list of 4 oscillators with

different frequency ranges has to be done by OP-

TION BYTE in order to reduce the consumption. In

this mode of the MO block, the resonator and the

load capacitances have to be connected as shown

in Figure 20 and have to be mounted 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, when selected via the OPTION

BYTE, are not stopped during the RESET phase

to avoid losing time in the oscillator start-up phase.

Figure 20. MO Crystal/Ceramic Resonator

OSC1

OSC2

EXTERNAL

ST7

SOURCE

OSC1

OSC2

LOAD

CAPACITANCES

ST7

CL1

CL0

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