P87LPC778 datasheet(40/79 Pages) PHILIPS

40 / 79 page

Philips Semiconductors

P87LPC778

CMOS single-chip 8-bit microcontroller

Product data

Rev. 01 — 31 March 2004

40 of 79

9397 750 12378

8.10.4

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. A clock output on the

X2 / P2.0 pin may be enabled when the on-chip RC oscillator is used.

8.10.5

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 VDD is above 4.5 V and

up to 10 MHz when VDD is below 4.5 V. 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.

8.10.6

Clock output

The P87LPC778 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 P87LPC778. When enabled, via the ENCLK bit in the P2M1

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.

Table 39:

Recommended oscillator capacitors for use with the high frequency oscillator option

Oscillator

Frequency

VDD = 2.7 V to 4.5 V

VDD = 4.5 V to 5.5 V

Lower Limit

Optimal Value

Upper Limit

Lower Limit

Optimal Value

Upper Limit

4 MHz

15 pF

33 pF

47 pF

15 pF

33 pF

68 pF

8 MHz

15 pF

33 pF

15 pF

33 pF

47 pF

16 MHz

15 pF

33 pF

20 MHz

15 pF

33 pF

The oscillator must be conﬁgured in one of the following modes: Low frequency crystal,

medium frequency crystal, or high frequency crystal.

(1) A series resistor may be required to limit crystal drive levels. This is especially important

for low frequency crystals (see text).

Fig 14. Using the crystal oscillator.

002aaa632

87LPC77x

quartz crystal or

ceramic resonator

[1]

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