Datasheet
Appendix A Electrical Characteristics
MC9S12E256 Data Sheet, Rev. 1.10
Freescale Semiconductor 585
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) f
OSC
0.5 — 16 MHz
1b C Crystal oscillator range (Pierce)
1
1
Depending on the crystal a damping series resistor might be necessary
f
OSC
0.5 — 40 MHz
2 P Startup Current i
OSC
100 — — µA
3 C Oscillator start-up time (Colpitts) t
UPOSC
—8
2
2
f
osc
= 4MHz, C = 22pF.
100
3
3
Maximum value is for extreme cases using high Q, low frequency crystals
ms
4 D Clock Quality check time-out t
CQOUT
0.45 2.5 s
5 P Clock Monitor Failure Assert Frequency f
CMFA
50 100 200 KHz
6 P External square wave input frequency
4
4
Only valid if Pierce oscillator/external clock mode is selected
f
EXT
0.5 — 50 MHz
7 D External square wave pulse width low
4
t
EXTL
9.5 — — ns
8 D External square wave pulse width high
4
t
EXTH
9.5 — — ns
9 D External square wave rise time
4
t
EXTR
—— 1ns
10 D External square wave fall time
4
t
EXTF
—— 1ns
11 D Input Capacitance (EXTAL, XTAL pins) C
IN
—7 pF
12 C DC Operating Bias in Colpitts Configuration on
EXTAL Pin
V
DCBIAS
— 1.1 — V
13 P EXTAL Pin Input High Voltage
4
V
IH,EXTAL
0.75*V
DDPLL
——V
T EXTAL Pin Input High Voltage
4
V
IH,EXTAL
——V
DDPLL
+ 0.3 V
14 P EXTAL Pin Input Low Voltage
4
V
IL,EXTAL
— — 0.25*V
DDPLL
V
T EXTAL Pin Input Low Voltage
4
V
IL,EXTAL
V
SSPLL
– 0.3 — — V
15 C EXTAL Pin Input Hysteresis
4
V
HYS,EXTAL
— 250 — mV