ST10F272B_12 STMICROELECTRONICS [STMicroelectronics], ST10F272B_12 Datasheet - Page 158

• Manufacturer Part Number: ST10F272B_12
• Description: 16-bit MCU with 256 Kbyte Flash memory and 12/20 Kbyte RAM
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Electrical characteristics
24.8.10
Note:
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contribution of the digital noise to the global jitter is widely taken into account in the curves
provided in
Figure 45. ST10F272 PLL jitter
PLL lock / unlock
During normal operation, if the PLL gets unlocked for any reason, an interrupt request to the
CPU is generated, and the reference clock (oscillator) is automatically disconnected from
the PLL input: in this way, the PLL goes into free-running mode, providing the system with a
backup clock signal (free running frequency F
crystal failure occurrence without risking to go in an undefined configuration: the system is
provided with a clock allowing the execution of the PLL unlock interrupt routine in a safe
mode.
The path between reference clock and PLL input can be restored only by a hardware reset,
or by a bidirectional software or watchdog reset event that forces the RSTIN pin low.
The external RC circuit on RSTIN pin shall be properly sized in order to extend the duration
of the low pulse to grant the PLL gets locked before the level at RSTIN pin is recognized
high: bidirectional reset internally drives RSTIN pin low for just 1024 TCL (definitively not
sufficient to get the PLL locked starting from free-running mode).
Figure
45.
Doc ID 11917 Rev 3
free
). This feature allows to recover from a
ST10F272B/ST10F272E