st10f272z2 STMicroelectronics, st10f272z2 Datasheet - Page 161

• Manufacturer Part Number: st10f272z2
• Description: 16-bit Mcu With 256 Kbyte Flash Memory And 20 Kbyte Ram
• Manufacturer: STMicroelectronics

ST10F272Z2
25.8.10
Note:
Figure 49. ST10F272Z2 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).
T
±5
±4
±3
±2
±1
JIT
0
0
200
16MHz
400
24MHz
N (CPU clock periods)
600
32MHz
free
40MHz
). This feature allows to recover from a
800
1000
Electrical characteristics
1200
64MHz
1400
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