Electrical characteristics
(4)
STM8S105xx
t
SU(HSE)
is the start-up time measured from the moment it is enabled (by software) to a stabilized 16
MHz oscillation is reached. This value is measured for a standard crystal resonator and it can vary
significantly with the crystal manufacturer.
Figure 20: HSE oscillator circuit diagram
Rm
f HSE to core
Lm
Cm
CO
CL1
OSCIN
RF
gm
Resonator
Resonator
Consumption
control
CL2
OSCOUT
STM8
HSE oscillator critical g
m
equation
g
mcrit
= (2 × Π × f
HSE
) × R
m
(2Co + C)
2
2
R
m
: Notional resistance (see crystal specification)
L
m
: Notional inductance (see crystal specification)
C
m
: Notional capacitance (see crystal specification)
Co: Shunt capacitance (see crystal specification)
C
L1
= C
L2
= C: Grounded external capacitance
g
m
>> g
mcrit
10.3.4
Internal clock sources and timing characteristics
Subject to general operating conditions for V
DD
and T
A
.
High speed internal RC oscillator (HSI)
Table 34: HSI oscillator characteristics
Symbol Parameter
f
HSI
Frequency
User-trimmed with
CLK_HSITRIMR register
for given V
DD
and T
A
conditions
Conditions
Min
Typ
16
1.0
Max
Unit
MHz
%
ACC
HSI
Accuracy of HSI
oscillator
78/127
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