L9805 datasheet(16/103 Pages) STMICROELECTRONICS

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L9805

3.2 OSCILLATOR SAFEGUARD

The L9805 contains an oscillator safe guard func-

tion.

This function provides a real time check of the

crystal oscillator generating a reset condition when

the clock frequency has anomalous value.

If fOSC<flow, a reset is generated.

If fOSC>fhigh, a reset is generated.

A flag in the Dedicated Control Status Register in-

dicates if the last reset is a safeguard reset.

At the output of reset state the safeguard is disa-

ble. To activate the safeguard SFGEN bit must be

set.

Notes: Following a reset, the safeguard is disa-

bled. Once activated it cannot be disabled, except

by a reset.

3.2.1 Dedicated Control Status Register

DCSR

Address 0022h - Read/Write

Reset Value:xx00 0000 (00h)

b6 = SGFH: Safeguard high flag. Set by an Oscil-

lator Safeguard Reset generated for frequency too

high, cleared by software (writing zero) or Power

On / Low Voltage Reset. This flag is useful for dis-

tinguishing Safeguard Reset, Power On / Low

Voltage Reset and Watchdog Reset.

b7 = SGFL: Safeguard low flag. Set by an Oscilla-

tor Safeguard Reset generated for frequency too

low, cleared by software (writing zero) or Power

On / Low Voltage Reset. This flag is useful for dis-

tinguishing Safeguard Reset, Power On / Low

Voltage Reset and Watchdog Reset.

b5 = SFGEN: Safeguard enable when set. It’s

cleared only by hardware after a reset.

b4 = CANDS: CAN Transceiver disable. When this

bit is set the CAN transceiver goes in Power Down

Mode and does not work until this bit is reset.

CANDS is 0 after reset so the standard condition is

with the transceiver enabled. This bit can be used

by application requiring low power consumption

(see Section 5.7 for details).

b3,b2,b1 = not used

b0 = PIEN: PWMI input enable. When set, the

PWMI input line is connected to Input Capture 2 of

Timer 2. Otherwise, ICAP2_2 is the alternate func-

tion of PA7. See Figure 31 for the explanation of

this function.

SGFL

SGFH

SFGEN

CANDS

PIEN

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