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Chapter 4
Clock Generator
Preliminary User’s Manual U17566EE1V2UM00
4.1.4
Start conditions
After any reset release, the ring oscillator is always selected as the clock
source. The oscillation stabilization time for the ring oscillator is ensured by
hardware. The CPU clock VBCLK is derived from the ring oscillator.
Several clocks are operating based on the ring oscillator clock after reset. As
soon as the main oscillator, which is started by the internal firmware, is stable
the source of these clocks is automatically changed to the main oscillator.
Therefore depending on the firmware operation and the main oscillator
stabilization time these clocks may already be operating with the main
oscillator, when the user’s program is started.
Internal firmware starts the main oscillator. PLL and SSCG remain stopped.
When the firmware passes control to the application software, software has to
ensure that the main oscillator has stabilized and to start the PLL and SSCG.
Note
Clock supply for most peripherals is not available unless the main oscillator
operates.
CPU access to peripherals that have no clock supply may cause system
deadlock.
Table 4-2
Clock Generator status after reset release
Item
Status
Remarks
Main oscillator
stopped
started by internal firmware
Sub oscillator
operates
Ring oscillator
operates
SSCG
stopped
PLL
stopped
VBCLK (CPU system)
operates
based on ring oscillator clock
IICLK
operates
based on ring/main oscillator clock
a
a)
Starts with ring oscillator, automatically changed to main oscillator, when main os-
cillator stable.
PCLK0, PCLK1
operates
based on ring/main oscillator clock
a
PCLK2…PCLK15
operates
based on ring/main oscillator clock
a
SPCLK0, SPCLK1
operates
based on ring/main oscillator clock
a
SPCLK2…SPCLK15
operates
based on ring/main oscillator clock
a
FOUTCLK
operates
based on ring/main oscillator clock
a
LCDCLK / WTCLK
operates
b
b)
If the reset was caused by Power-On Clear (POC) or external RESET, the
clock source for LCDCLK and WTCLK is set to ring oscillator. If the reset
was caused by a different source, the clock selection for LCDCLK / WT-
CLK remains unchanged.
based on ring/main oscillator clock
a
WDTCLK
operates
based on ring/main oscillator clock
a
WCTCLK
operates
based on ring/main oscillator clock
a
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