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7.8
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 at half
the oscillator frequency. These signals define the internal phases, states and machine cycles, as
described in chapter 3.
7.8.1
Crystal Oscillator Mode
Figure 7-48 shows the recommended oscillator circuit.
Figure 7-48
Recommended Oscillator Circuit for the SAB 80(C)515/80(C)535
In this application the on-chip oscillator is used as a crystal-controlled, positive-reactance oscillator
(a more detailed schematic is given in figure 7-49 and 7-51). 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 30 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. lf a ceramic resonator is used,
are normally selected to be different values. We recommend consulting the manufacturer of the
ceramic resonator for value specifications of these capacitors.
7.8.2
Driving for External Source
The SAB 80(C)515/80(C)535 can be driven from an external oscillator.
Please note that there is a difference between driving MYMOS and ACMOS devices from an
external clock source.
Semiconductor Group
On-Chip Peripheral Components
*
107
C
C
and
1
2
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