Functional Description
204
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
System Control
The internal system clock (SysClk), is derived from any of the preceding sources. An internal PLL can also
be used by the PIOSC or MOSC clock to generate the system clock and peripheral clocks.
shows how the various clock sources can be used in a system.
(1)
LFIOSC frequency is characterized as 33 kHz nominal, 10 kHz minimum, and 90 kHz maximum.
Table 4-2. Clock Source Options
Clock Source
Drive PLL
Capability?
PLL Enabled, RSCLKCFG Bit
Encodings
SysClk
Generation
Capability?
SysClk Generation Enabled,
RSCLKCFG Bit Encodings
PIOSC
Yes
USEPLL = 1, PLLSRC = 0x0
Yes
USEPLL = 0, OSCSRC = 0x0
MOSC
Yes
USEPLL = 1, PLLSRC = 0x3
Yes
USEPLL = 0, OSCSRC = 0x3
LFIOSC
(1)
No
–
Yes
USEPLL = 0, OSCSRC = 0x2
RTCOSC (32.768-kHz
oscillator or HIB LFIOSC)
No
–
Yes
USEPLL = 0, OSCSRC = 0x4
4.1.5.2
Clock Configuration
The Run and Sleep Mode Configuration (RSCLKCFG) register provides control for the system clock in run
and sleep mode. The DSCLKCFG register specifies the behavior of the clock system while in deep-sleep
mode. These registers control the following clock functionality:
•
Source of system clock in run and sleep mode
•
Source of system clock in deep-sleep mode
•
Enabling and disabling of PLL-derived system clock
•
Clock divisors for PLL or oscillator, depending on what is enabled
•
Enabling of memory timing parameters for flash
Providing further configuration, the PLL Frequency n (PLLFREQn) registers allow multiplication or division
of the PLL VCO frequency (f
VCO
) by programmable values, depending on the system clock speed required.
lists the state of the clock sources following a POR.
Table 4-3. Clock Source State Following POR
Clock Source
POR State
PLL
Disabled or powered off
MOSC
Disabled or powered off
LFIOSC
Enabled
PIOSC
Enabled
HIB RTCOSC
Disabled
shows the logic for the main clock tree. The peripheral blocks are driven by the system clock
signal and can be individually enabled or disabled.
NOTE:
The clock sources in
include a superset of peripherals available in the family.
Some peripheral clock sources may not be present on your specific device.