Table 35. Low-Speed External User Clock Characteristics; Figure 16. Low-Speed External Clock Source Ac Timing Diagram - STMicroelectronics STM32F042G4 Manual

Electrical characteristics
Low-speed external user clock generated from an external source
In bypass mode the LSE oscillator is switched off and the input pin is a standard GPIO.
The external clock signal has to respect the I/O characteristics in
the recommended clock input waveform is shown in
Symbol
f User external clock source frequency
LSE_ext
V OSC32_IN input pin high level voltage
LSEH
V OSC32_IN input pin low level voltage
LSEL
t
w(LSEH)
OSC32_IN high or low time
t
w(LSEL)
t
r(LSE)
OSC32_IN rise or fall time
t
f(LSE)
1. Guaranteed by design, not tested in production.
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Table 35. Low-speed external user clock characteristics

(1)
Parameter

Figure 16. Low-speed external clock source AC timing diagram

DocID025832 Rev 2
Figure
Conditions Min
-
0.7 V
DDIOx
V
SS
450
-
STM32F042xx
Section 6.3.14. However,
16.
Typ Max
32.768 1000
- V
DDIOx
- 0.3 V
DDIOx
- -
- 50
Unit
kHz
V
ns