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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.
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.
OSCOUT must not be used to drive external cir-
cuits.
When the oscillator is stopped, OSCOUT goes
high impedance.
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.
To exit the HALT condition and restart the oscilla-
tor, an external RESET pulse is required, having a
a minimum duration of 12ms, as illustrated in Fig-
ure 41
It should be noted that, if the Watchdog function is
enabled, a HALT instruction will not disable the os-
cillator. This to avoid stopping the Watchdog if a
HALT
code is executed in error. When this occurs,
the CPU will be reset when the Watchdog times
out or when an external reset is applied.
Table 15. Oscillator Transconductance
Figure 37. Crystal Oscillator
Table 16. Crystal Internal Resistance(
) (5V
Op.)
Table 17. Crystal Internal Resistance(
) (3V
Op.)
Legend:
CL1, CL2: Maximum Total Capacitance on pins OSCIN
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).
Note: The tables are relative to the fundamental quartz
crystal only (not ceramic resonator).
Figure 38. Internal Oscillator Schematic
Figure 39. External Clock
gm
Min
Typ
Max
5V Operation
mA/V
0.77
1.5
2.4
3V Operation
0.42
0.73
1.47
OSCIN
OSCOUT
CL1
CL2
ST9
CRYSTAL CLOCK
1M
*Recommended for oscillator stability
C1=C2
Freq.
56pF
47pF
33pF
22pF
5 Mhz
110
120
210
340
4 Mhz
150
200
330
510
3 Mhz
270
350
560
850
C1=C2
Freq.
56pF
47pF
33pF
22pF
5 Mhz
35
45
75
120
4 Mhz
55
70
125
195
3 Mhz
100
135
220
350
HALT
OSCIN
OSCOUT
RIN
ROUT
R
OSCIN
OSCOUT
CLOCK
INPUT
NC
EXTERNAL CLOCK
ST9
9