Philips Semiconductors Preliminary data
P87LPC769
Low power, low price, low pin count (20 pin)
microcontroller with 4 kB OTP 8-bit A/D, and DAC
2002 Mar 12
27
Oscillator
The P87LPC769 provides several user selectable oscillator options,
allowing optimization for a range of needs from high precision to
lowest possible cost. These are configured when the EPROM is
programmed. Basic oscillator types that are supported include: low,
medium, and high speed crystals, covering a range from 20 kHz to
10 MHz; ceramic resonators; and on-chip RC oscillator.
Low Frequency Oscillator Option
This option supports an external crystal in the range of 20 kHz to 100 kHz.
Table 6 shows capacitor values that may be used with a quartz crystal in this mode.
Table 6. Recommended oscillator capacitors for use with the low frequency oscillator option
Oscillator
V
DD
= 4.5 to 5.5 V
Frequency
Lower Limit Optimal Value Upper Limit
20 kHz 33 pF 33 pF 47 pF
32 kHz 33 pF 33 pF 47 pF
100 kHz 15 pF 15 pF 33 pF
Medium Frequency Oscillator Option
This option supports an external crystal in the range of 100 kHz to 4 MHz. Ceramic resonators are also supported in this configuration.
Table 7 shows capacitor values that may be used with a quartz crystal in this mode.
Table 7. Recommended oscillator capacitors for use with the medium frequency oscillator option
V
DD
= 4.5 to 5.5 V
u
Lower Limit Optimal Value Upper Limit
100 kHz 33 pF 33 pF 47 pF
1 MHz 15 pF 15 pF 33 pF
4 MHz 15 pF 15 pF 33 pF
High Frequency Oscillator Option
This option supports an external crystal in the range of 4 to 10 MHz. Ceramic resonators are also supported in this configuration.
Table 8 shows capacitor values that may be used with a quartz crystal in this mode.
Table 8. Recommended oscillator capacitors for use with the high frequency oscillator option
Oscillator
V
DD
= 4.5 to 5.5 V
Frequency
Lower Limit Optimal Value Upper Limit
4 MHz 15 pF 33 pF 68 pF
8 MHz 15 pF 33 pF 47 pF
On-Chip RC Oscillator Option
The on-chip RC oscillator option has a typical frequency of 6 MHz
and can be divided down for slower operation through the use of the
DIVM register. Note that the on-chip oscillator has a ±25% frequency
tolerance and for that reason may not be suitable for use in some
applications. A clock output on the X2/P2.0 pin may be enabled
when the on-chip RC oscillator is used.
External Clock Input Option
In this configuration, the processor clock is input from an external
source driving the X1/P2.1 pin. The rate may be from 0 Hz up to
10 MHz. When the external clock input mode is used, the X2/P2.0 pin
may be used as a standard port pin. A clock output on the X2/P2.0 pin
may be enabled when the external clock input is used.
Clock Output
The P87LPC769 supports a clock output function when either the
on-chip RC oscillator or external clock input options are selected.
This allows external devices to synchronize to the P87LPC769.
When enabled, via the ENCLK bit in the P2M1 register, the clock
output appears on the X2/CLKOUT pin whenever the on-chip
oscillator is running, including in Idle mode. The frequency of the
clock output is 1/6 of the CPU clock rate. If the clock output is not
needed in Idle mode, it may be turned off prior to entering Idle,
saving additional power. The clock output may also be enabled
when the external clock input option is selected.
