P87LPC768 NXP Semiconductors, P87LPC768 Datasheet - Page 32

• Manufacturer Part Number: P87LPC768
• Description: The P87LPC768 is a 20-pin single-chip microcontroller designed forlow pin count applications demanding high-integration, low costsolutions over a wide range of performance requirements
• Manufacturer: NXP Semiconductors

DIVM register. Note that the on-chip oscillator has a 25% frequency
Philips Semiconductors
Oscillator
The P87LPC768 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
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
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
High Frequency Oscillator Option
This option supports an external crystal in the range of 4 to 20 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
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
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
20 MHz when V
below 4.5 V. When the external clock input mode is used, the X2/P2.0
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Frequency
Frequency
Oscillator
Oscillator
100 kHz
16 MHz
20 MHz
20 kHz
32 kHz
Oscillator Freq ency
Oscillator Frequency
4 MHz
8 MHz
100 kHz
1 MHz
4 MHz
DD
is above 4.5 V and up to 10 MHz when V
Lower Limit
Lower Limit
15 pF
15 pF
15 pF
15 pF
15 pF
–
–
V
V
DD
DD
Optimal Value
Optimal Value
= 2.7 to 4.5 V
= 2.7 to 4.5 V
Lower Limit
15 pF
15 pF
15 pF
33 pF
15 pF
–
–
33 pF
15 pF
15 pF
DD
is
Upper Limit
Upper Limit
33 pF
33 pF
33 pF
47 pF
33 pF
30
–
–
programmed. Basic oscillator types that are supported include: low,
medium, and high speed crystals, covering a range from 20 kHz to
20 MHz; ceramic resonators; and on-chip RC oscillator.
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 P87LPC768 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 P87LPC768.
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.
V
DD
Optimal Value
= 2.7 to 4.5 V
Lower Limit
Lower Limit
33 pF
15 pF
15 pF
33 pF
33 pF
15 pF
15 pF
15 pF
15 pF
15 pF
V
V
DD
DD
Optimal Value
Optimal Value
= 4.5 to 6.0 V
= 4.5 to 6.0 V
33 pF
33 pF
15 pF
33 pF
33 pF
15 pF
15 pF
Upper Limit
P87LPC768
47 pF
33 pF
33 pF
Upper Limit
Upper Limit
Preliminary data
47 pF
47 pF
33 pF
68 pF
47 pF
33 pF
33 pF