TC1784
System Control Unit (SCU)
User´s Manual
3-9
V1.1, 2011-05
32-bit SCU, V1.18
The output frequency is given by
(3.2)
Freerunning Mode
In Freerunning Mode the base frequency output of the Voltage Controlled Oscillator
(VCO)
f
VCObase
is only divided down by a factor K2.
The output frequency is given by
(3.3)
Oscillator Watchdog (OSC_WDT)
The oscillator watchdog monitors the incoming clock frequency
f
OSC
from OSC. A stable
and defined input frequency is a mandatory requirement for operation in both Prescaler
Mode and Normal Mode. For operation in Freerunning Mode no
f
OSC
input frequency is
required. Therefore this mode is selected automatically after each System Reset. In
addition for the Normal Mode it is required that the input frequency
f
OSC
is in a certain
frequency range to obtain a stabile master clock from the VCO part.
The expected input frequency is selected via the bit field OSCCON.OSCVAL. The
OSC_WDT checks for too low frequencies and for too high frequencies.
The frequency that is monitored is
f
OSCREF
which is derived for
f
OSC
.
(3.4)
The divider value OSCCON.OSCVAL has to be selected in a way that
f
OSCREF
is
2.5 MHz.
Note: f
OSCREF
has to be within the range of 2 MHz to 3 MHz and should be as close as
possible to 2.5 MHz.
Before configuring the OSC_WDT function all the trap options should be disabled in
order to avoid unintended traps. Thereafter the value of OSCCON.OSCVAL can be
changed. Then the OSC_WDT should be reset by setting OSCCON.OSCRES. This
requests the start of OSC_WDT monitoring with the new configuration. When the
expected positive monitoring results of OSCCON.PLLLV and / or OSCCON.PLLHV are
set the input frequency is within the expected range. As setting OSCCON.OSCRES
fPLL
fOSC
K1
--------------
=
fPLL
fVCObase
K2
---------------------------
=
f
OSCR EF
f
OSC
OSCVAL 1
+
-----------------------------------
=
Summary of Contents for TC1784
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Page 950: ...TC1784 Direct Memory Access Controller DMA User s Manual 11 132 V1 1 2011 05 DMA V3 03 ...
Page 1949: ...TC1784 General Purpose Timer Array GPTA v5 User s Manual 21 297 V1 1 2011 05 GPTA v5 V1 14 ...
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