Electrical characteristics
STM32F042x4 STM32F042x6
60/117
DocID025832 Rev 5
6.3.6
Wakeup time from low-power mode
The wakeup times given in
are the latency between the event and the execution of
the first user instruction. The device goes in low-power mode after the WFE (Wait For
Event) instruction, in the case of a WFI (Wait For Interruption) instruction, 16 CPU cycles
must be added to the following timings due to the interrupt latency in the Cortex M0
architecture.
The SYSCLK clock source setting is kept unchanged after wakeup from Sleep mode.
During wakeup from Stop or Standby mode, SYSCLK takes the default setting: HSI 8 MHz.
The wakeup source from Sleep and Stop mode is an EXTI line configured in event mode.
The wakeup source from Standby mode is the WKUP1 pin (PA0).
All timings are derived from tests performed under the ambient temperature and supply
voltage conditions summarized in
Table 21: General operating conditions
6.3.7 External
clock
source characteristics
High-speed external user clock generated from an external source
In bypass mode the HSE oscillator is switched off and the input pin is a standard GPIO.
The external clock signal has to respect the I/O characteristics in
. However,
the recommended clock input waveform is shown in
Figure 15: High-speed external clock
.
Table 33. Low-power mode wakeup timings
Symbol
Parameter
Conditions
Typ @V
DD =
V
DDA
Max Unit
= 2.0 V = 2.4 V = 2.7 V
= 3 V
= 3.3 V
t
WUSTOP
Wakeup from Stop
mode
Regulator in run
mode
3.2
3.1
2.9
2.9
2.8
5
µs
Regulator in low
power mode
7.0
5.8
5.2
4.9
4.6
9
t
WUSTANDBY
Wakeup from
Standby mode
-
60.4
55.6
53.5
52
51
-
t
WUSLEEP
Wakeup from Sleep
mode
-
4 SYSCLK cycles
-
Table 34. High-speed external user clock characteristics
Symbol
Parameter
(1)
Min
Typ
Max
Unit
f
HSE_ext
User external clock source frequency
-
8
32
MHz
V
HSEH
OSC_IN input pin high level voltage
0.7 V
DDIOx
-
V
DDIOx
V
V
HSEL
OSC_IN input pin low level voltage
V
SS
-
0.3 V
DDIOx
t
w(HSEH)
t
w(HSEL)
OSC_IN high or low time
15
-
-
ns
t
r(HSE)
t
f(HSE)
OSC_IN rise or fall time
-
-
20
