saf-xc888cm-8ffi5v Infineon Technologies Corporation, saf-xc888cm-8ffi5v Datasheet - Page 82

• Manufacturer Part Number: saf-xc888cm-8ffi5v
• Description: 8-bit Single-chip Microcontroller
• Manufacturer: Infineon Technologies Corporation

Table 25
Table 25
3.8.1
The oscillator circuit, a Pierce oscillator, is designed to work with both, an external crystal
oscillator or an external stable clock source. It basically consists of an inverting amplifier
and a feedback element with XTAL1 as input, and XTAL2 as output.
When using a crystal, a proper external oscillator circuitry must be connected to both
pins, XTAL1 and XTAL2. The crystal frequency can be within the range of 4 MHz
to 12 MHz. Additionally, it is necessary to have two load capacitances
depending on the crystal type, a series resistor
may be temporarily inserted to measure the oscillation allowance (negative resistance)
of the oscillator circuitry.
and
resistance evaluation and for non-productive systems. The exact values and related
operating range are dependent on the crystal frequency and have to be determined and
optimized together with the crystal vendor using the negative resistance method.
Oscillation measurement with the final target system is strongly recommended to verify
the input amplitude at XTAL1 and to determine the actual oscillation allowance (margin
negative resistance) for the oscillator-crystal system.
When using an external clock signal, the signal must be connected to XTAL1. XTAL2 is
left open (unconnected).
The oscillator can also be used in combination with a ceramic resonator. The final
circuitry must also be verified by the resonator vendor.
recommended external oscillator circuitries for both operating modes, external crystal
mode and external input clock mode.
Data Sheet
f
150
100
VCOmin
C
X2
values shown in
shows the VCO range for the XC886/888.
Recommended External Oscillator Circuits
VCO Range
f
200
150
VCOmax
R
Q
Figure 25
values are typically specified by the crystal vendor. The
f
20
10
can be used as starting points for the negative
VCOFREEmin
75
R
X2
, to limit the current. A test resistor
80
80
f
VCOFREEmax
Functional Description
Figure 25
XC886/888CLM
C
X1
and
Unit
MHz
MHz
V1.1, 2009-01
shows the
C
X2
, and
C
R
X1
Q