ST90158 - RESET AND CLOCK CONTROL UNIT (RCCU)
6.5 OSCILLATOR CHARACTERISTICS
The on-chip oscillator circuit uses an inverting gate
circuit with tri-state output.
Table 16. Crystal Internal Resistance(Ω) (5V
Op.)
Notes: It is recommended to place the quartz or
crystal as close as possible to the ST9 to reduce
the parasitic capacitance. At low temperature,
frost and humidity might prevent a correct start-up
of the oscillator.
C =C
Freq.
56pF
47pF
33pF
22pF
1
2
5 Mhz
4 Mhz
3 Mhz
110
150
270
120
200
350
210
330
560
340
510
850
OSCOUT must not be used to drive external cir-
cuits.
Table 17. Crystal Internal Resistance(Ω) (3V
Op.)
When the oscillator is stopped, OSCOUT goes
high impedance.
C =C
56pF
47pF
33pF
22pF
1
2
Freq.
In Halt mode, set by means of the HALT instruc-
tion, the parallel resistor, R, is disconnected and
the oscillator is disabled, forcing the internal clock,
CLOCK1, to a high level, and OSCOUT to a high
impedance state.
5 Mhz
4 Mhz
3 Mhz
35
55
45
70
75
120
195
350
125
220
100
135
Legend:
To exit the HALTcondition and restart the oscilla-
tor, an external RESET pulse is required, having a
a minimum duration of 12ms, as illustrated in Fig-
ure 41
C
, C : Maximum Total Capacitance on pins OSCIN
L1
L2
and OSCOUT (the value includes the external capaci-
tance tied to the pin CL1 and CL2 plus the parasitic capac-
itance of the board and of the device).
It should be noted that, if the Watchdog function is
enabled, a HALTinstruction will not disable the os-
cillator. This to avoid stopping the Watchdog if a
HALTcode is executed in error. When this occurs,
the CPU will be reset when the Watchdog times
out or when an external reset is applied.
Note: The tables are relative to the fundamental quartz
crystal only (not ceramic resonator).
Figure 38. Internal Oscillator Schematic
HALT
Table 15. Oscillator Transconductance
gm
Min
0.77
0.42
Typ
1.5
Max
2.4
5V Operation
3V Operation
mA/V
0.73
1.47
R
Figure 37. Crystal Oscillator
R
R
OUT
IN
CRYSTAL CLOCK
OSCIN
OSCOUT
ST9
OSCIN
OSCOUT
Figure 39. External Clock
EXTERNAL CLOCK
C
C
L1
ST9
L2
OSCIN
OSCOUT
NC
1MΩ
*Recommended for oscillator stability
CLOCK
INPUT
76/199
9
ETC [ ETC ]
