L9803 STMicroelectronics, L9803 Datasheet - Page 20

• Manufacturer Part Number: L9803
• Description: Super Smart Power Motor Driver With 8-bit Mcu, Ram, Eeprom, Adc, Wdg, Timers, Pwm And H-bridge Driver
• Manufacturer: STMicroelectronics

Clocks, Reset, Interrupts & Power saving modes
3.2
Note:
3.2.1
20/126
Figure 8.
Oscillator safeguard
The L9803 contains an oscillator safe guard function.
This function provides a real time check of the crystal oscillator generating a reset condition
when the clock frequency has anomalous value.
If f
If f
A flag in the Dedicated Control Status Register indicates if the last reset is a safeguard
reset.
At the output of reset state the safeguard is disable. To activate the safeguard SFGEN bit
must be set.
Following a reset, the safeguard is disabled. Once activated it cannot be disabled, except by
a reset.
Dedicated Control Status Register
DCSR
Address 0022h - Read/Write
Reset Value:xx00 0000 (00h)
b6 = SGFH: Safeguard high flag. Set by an Oscillator Safeguard Reset generated for
frequency too high, cleared by software (writing zero) or Power On / Low Voltage Reset.
CPU CLK
b1 : b2
OSC
OSC
OSC/2
OSC/4
OSC/8
SGFL
MISCELLANEOUS REGISTER
b0
<f
>f
low
high,
, a reset is generated.
Timing Diagram for Internal CPU Clock Frequency transitions
a reset is generated.
SGFH
New frequency
requested
1
00
SFGEN
01
New frequency
active when
osc/4 & osc/8 = 0
CANDS
Normal mode
requested
b3
1 0
b2
Normal mode active
(osc/4 - osc/8 stopped)
b1
VR02062B
PIEN
L9803