User’s Manual
5-6
05.99
Reset / System Clock
C513AO
5.4
Oscillator and Clock Circuit
XTAL1 and XTAL2 are the input and output of a single-stage on-chip inverter which can be
configured with off-chip components as a pierce oscillator. The oscillator, in any case, drives the
internal clock generator. The clock generator provides the internal clock signals to the chip. These
signals define the internal phases, states, and machine cycles.
Figure 5-4 shows the recommended oscillator circuit.
Figure 5-4
Recommended Oscillator Circuit
In this application, the on-chip oscillator is used as a crystal-controlled, positive-reactance oscillator
(a more detailed schematic is given in Figure 5-5). lt is operated in its fundamental response mode
as an inductive reactor in parallel resonance with a capacitor external to the chip. The crystal
specifications and capacitances are non-critical. In this circuit, 20 pF can be used as single
capacitance at any frequency together with a good quality crystal. A ceramic resonator can be used
in place of the crystal in cost-critical applications. If a ceramic resonator is used, the two capacitors
normally will have different values, dependent on the oscillator frequency. We recommend
consulting the manufacturer of the ceramic resonator for value specifications of these capacitors.
MCS04014
XTAL2
C513AO
XTAL1
3.5-16 MHz
C
C
C
= 20 pF ±10 pF for crystal operation
