MC9S12E256 Datasheet, PDF (573/602 Pages) Freescale Semiconductor, Inc – HCS12 Microcontrollers

Appendix A Electrical Characteristics
A.3.2 Oscillator
The device features an internal Colpitts and Pierce oscillator. The selection of Colpitts oscillator or Pierce
oscillator/external clock depends on the XCLKS signal which is sampled during reset. Pierce
oscillator/external clock mode allows the input of a square wave. Before asserting the oscillator to the
internal system clocks the quality of the oscillation is checked for each start from either power-on, STOP
or oscillator fail. t_CQOUT specifies the maximum time before switching to the internal self clock mode after
POR or STOP if a proper oscillation is not detected. The quality check also determines the minimum
oscillator start-up time t_UPOSC. The device also features a clock monitor. A Clock Monitor Failure is
asserted if the frequency of the incoming clock signal is below the Assert Frequency f_CMFA.
Table A-12. Oscillator Characteristics
Conditions are shown in Table A-4 unless otherwise noted
Num C
Rating
Symbol
Min
Typ
Max
Unit
1a C Crystal oscillator range (Colpitts)
1b C Crystal oscillator range (Pierce) ¹
f_OSC
0.5
—
f_OSC
0.5
—
16
MHz
40
MHz
2 P Startup Current
3 C Oscillator start-up time (Colpitts)
i_OSC
100
—
—
µA
t_UPOSC
—
8²
100³
ms
4 D Clock Quality check time-out
t_CQOUT
0.45
2.5
s
5 P Clock Monitor Failure Assert Frequency
6 P External square wave input frequency ⁴
7 D External square wave pulse width low⁴
8 D External square wave pulse width high⁴
9 D External square wave rise time⁴
10 D External square wave fall time⁴
f_CMFA
50
100
200
KHz
f_EXT
0.5
—
50
MHz
t_EXTL
9.5
—
—
ns
t_EXTH
9.5
—
—
ns
t_EXTR
—
—
1
ns
t_EXTF
—
—
1
ns
11 D Input Capacitance (EXTAL, XTAL pins)
C_IN
—
7
pF
12 C DC Operating Bias in Colpitts Configuration on
V_DCBIAS
—
1.1
—
V
EXTAL Pin
13 P EXTAL Pin Input High Voltage⁴
V_IH,EXTAL 0.75*V_DDPLL
—
—
V
T EXTAL Pin Input High Voltage⁴
V_IH,EXTAL
—
—
V_DDPLL + 0.3 V
14 P EXTAL Pin Input Low Voltage⁴
V_IL,EXTAL
—
—
0.25*V_DDPLL V
T EXTAL Pin Input Low Voltage⁴
V_IL,EXTAL V_SSPLL – 0.3
—
—
V
15 C EXTAL Pin Input Hysteresis⁴
V_HYS,EXTAL
—
250
—
mV
1 _{Depending on the crystal a damping series resistor might be necessary}
2 _{fosc = 4MHz, C = 22pF.}
3 _{Maximum value is for extreme cases using high Q, low frequency crystals}
4 _{Only valid if Pierce oscillator/external clock mode is selected}
MC9S12E256 Data Sheet, Rev. 1.08
Freescale Semiconductor
573