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UPGRADING FROM ST625X/6XB TO ST625X/6XC

Figure 2. OSG Filtering Function

1.1.2.1 Low Frequency Auxiliary Oscillator (LFAO)

The Low Frequency Auxiliary Oscillator has three main purposes. Firstly, it can be used to re-

duce power consumption in non timing critical routines. Secondly, it offers a fully integrated

system clock, without any external components. Lastly, it acts as a backup oscillator in case of

main oscillator failure.

This oscillator is available when the OSG option is selected in the option byte. In this case, it

automatically starts one of its periods after the first missing edge of the main oscillator, what-

ever the reason for the failure (main oscillator defective, no clock circuitry provided, main os-

cillator switched off...). See Figure 3.

Please note that the A/D converter accuracy is decreased, since the internal frequency is

below 1.2 MHz.

Figure 3. LFAO Oscillator Function

MAIN OSCILLATOR

STOPS

MAIN OSCILLATOR

RESTARTS

INTERNAL CLOCK DRIVEN BY LFAO