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P87LPC779 Fiches technique(PDF) 35 Page - NXP Semiconductors |
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P87LPC779 Fiches technique(HTML) 35 Page - NXP Semiconductors |
35 / 74 page Philips Semiconductors P87LPC779 CMOS single-chip 8-bit microcontroller Product data Rev. 02 — 03 May 2004 35 of 74 9397 750 13213 © Koninklijke Philips Electronics N.V. 2004. All rights reserved. 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 P87LPC779 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 P87LPC779. 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. Table 27: 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 6.0 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 15 pF 33 pF 15 pF 33 pF 47 pF 16 MHz - - - 15 pF 15 pF 33 pF 20 MHz - - - 15 pF 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 X1 X2 quartz crystal or ceramic resonator [1] |
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