User Manual
103
Rev. 1.1
2019-03-18
TLE984xQX
Microcontroller with LIN and Power Switches for Automotive Applications
System Control Unit - Digital Modules (SCU-DM)
7.3.4.2
Startup Control for System Clock
Typically when the TLE984xQX starts up after reset, the LP_CLK is selected by hardware to provide the system
frequency
f
SYS
. CPU runs based on this system frequency during startup operation by boot firmware (unless
otherwise specified and configured by firmware). Meanwhile, the system clock input is switched to the PLL
output. With user boot configuration, the PLL is configured with internal oscillator (5 MHz) as input, by default.
User code can modify the default PLL configuration as required.
The exception to the above is with a reset that does not reset the clock system: soft reset. With this reset, the
previous user configuration of PLL and clock system is retained across the reset.
Note:
In the event the PLL fails to lock during startup operation, the LP_CLK continues to provide the
system clock input. The system clock input source is indicated by the register bit field
SYSCON0.SYSCLKSEL.
7.3.5
External Clock Output
An external clock output is provided as CLKOUT. This output clock can be enabled/disabled via bit COCON.EN.
One of three clock sources (
f
CCLK
or
f
SYS
/n or
f
OSC
) can be selected for output, configured via bit fields
COCON.COUTS1 and COUTS0.
If COUTS1 = 0 (independent on COUTS0), the output clock is
f
CCLK
. Otherwise, if COUTS0 = 0, the output clock
is from oscillator output frequency; if COUTS0 = 1, the clock output frequency is chosen by the bit field COREL
which selects the n divider factor on
f
SYS
. Under this selection, the clock output frequency can further be
divided by 2 using a toggle latch (TLEN = 1), the resulting output frequency has 50% duty cycle.