1997 Mar 14
51
Philips Semiconductors
Product specification
Low voltage 8-bit microcontrollers with
UART, I
2
C-bus and ADC
P80CL580; P83CL580
18 OSCILLATOR CIRCUITRY
The on-chip oscillator circuitry of the P8xCL580 is a
single-stage inverting amplifier biased by an internal
feedback resistor. The oscillator circuit is shown in Fig.30.
For operation as a standard quartz oscillator, no external
components are needed, except for the 32 kHz option.
When using external capacitors, ceramic resonators, coils
and RC networks to drive the oscillator, five different
configurations are supported (see Table 48 and Fig.29).
In the Power-down mode the oscillator is stopped and
XTAL1 is pulled HIGH. The oscillator invertor is switched
off to ensure no current will flow regardless of the voltage
at XTAL1, for configurations (a), (b), (c), (d), (e) and (g) of
Fig.29.
To drive the device with an external clock source, apply the
external clock signal to XTAL1, and leave XTAL2 to float,
as shown in Fig.29(f). There are no requirements on the
duty cycle of the external clock, since the input to the
internal clocking circuitry is buffered by a flip-flop.
Various oscillator options are provided for optimum
on-chip oscillator performance; these are specified in
Table 48 and shown in Fig.29. The required option should
be stated when ordering.
Table 48
Oscillator options
OPTION
APPLICATION
Oscillator 1
For 32 kHz clock applications with external trimmer for frequency adjustment. A 4.7 M
bias resistor
is needed for use in parallel with the crystal; see Fig.29(c).
Low-power, low-frequency operations using LC components; see Fig.29(e).
Medium frequency range applications.
High frequency range applications.
RC oscillator configuration; see Figs 29(g) and 31.
Oscillator 2
Oscillator 3
Oscillator 4
RC oscillator
handbook, full pagewidth
MLA577
VDD
XTAL1
XTAL2
(d)
XTAL1
XTAL2
(e)
XTAL1
XTAL2
(f)
XTAL1
XTAL2
(g)
n.c.
n.c.
XTAL1
XTAL2
(b)
XTAL1
XTAL2
(c)
XTAL1
XTAL2
(a)
STANDARD
QUARTZ
OSCILLATOR
QUARTZ OSCILLATOR
WITH EXTERNAL
CAPACITORS
32 kHz
OSCILLATOR
CERAMIC
RESONATOR
LC - OSCILLATOR
EXTERNAL CLOCK
RC - OSCILLATOR
Fig.29 Oscillator configurations.