C508_01 Datasheet, PDF (64/267 Pages) Infineon Technologies AG – 8-Bit CMOS Microcontroller

C508
Reset and System Clock Operation
When software power-down mode is entered, the PLL is powered down together with the
RC oscillator and the on-chip oscillator. In this mode, the PLL is marked unlocked;
however, no internal resets will be generated.
5.6
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 such 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 5-6 shows the recommended oscillator circuit.
Crystal Oscillator Mode
C
XTAL1
5-10 MHz
C
C508
XTAL2
C = 20 pF + 10 pF for crystal operation
(incl. Stray Capacitance)
Driving from External Source
External Oscillator
Signal
XTAL1
N.C.
XTAL2
MCS04034
Figure 5-6 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 5-7). The on-chip
oscillator is operated in its fundamental response mode as an inductive reactor in parallel
resonance with a capacitor external to the chip. 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. It is recommended that the manufacturer of the ceramic resonator
be consulted for value specifications of these capacitors.
User’s Manual
5-8
2001-05