C505_9708 SIEMENS [Siemens Semiconductor Group], C505_9708 Datasheet - Page 59

• Manufacturer Part Number: C505_9708
• Description: 8-Bit CMOS Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

5.4
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 have different values depending on the oscillator frequency. We recommend consulting
the manufacturer of the ceramic resonator for value specifications of these capacitors.
Semiconductor Group
Oscillator and Clock Circuit
C = 20 pF 10 pF for crystal operation
2 - 20
MHz
C
C
5-6
XTAL1
XTAL2
C505
MCS03292
System Reset
C505 / C505C
1997-08-01