TC1796 Datasheet, PDF (77/134 Pages) Infineon Technologies AG – 32-Bit Single-Chip Microcontroller TriCore

TC1796
Functional Description
are derived from f_VCO only by the K-Divider. In this mode, the system clock f_SYS can
be equal to f_CPU or f_CPU/2.
XTAL1
XTAL2
Main
Osc.
Circuit
f_OSC
Clock Generation Unit (CGU)
P-
Divider
≥1
f_P
f_N
Phase
Detect.
VCO
M
f_VCO
U
X
f_CPU
Clock
Output
f_SYS
Control
K-
Divider
Osc.
Run
Detect.
PLL
PLL
Lock
Detect.
N-
Divider
BYPASS
P5.3 /
TXD1A
Oscillator Control Register
OSC_CON
PLL Clock Control and Status Register
PLL_CLC
System Control Unit (SCU)
MCB05600
Figure 19 Clock Generation Unit
Recommended Oscillator Circuits
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 25 MHz. Additionally are necessary, two load capacitances C_X1 and C_X2, and
depending on the crystal type a series resistor R_X2 to limit the current. A test resistor R_Q
may be temporarily inserted to measure the oscillation allowance (negative resistance)
of the oscillator circuitry. R_Q values are typically specified by the crystal vendor. The C_X1
and C_X2 values shown in Figure 20 can be used as starting points for the negative
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
Data Sheet
77
V1.0, 2008-04