■ The PHY receives the main oscillator (MOSC) which must be 25 MHz ± 50 ppm for proper
operation. The MOSC source can be a single-ended source or a crystal.
PWM Clock Control
The
PWMCC
register can be used to select the System Clock as the PWM clock source or a divided
System Clock. For more information, see page 1747.
Other Peripheral Clock Control
In the UART and QSSI Clock Control Registers, users can choose between the system clock
(SysClk), which is the default source for the baud clock, and an alternate clock. Note that there may
be special considerations when configuring the baud clock.
Optional Clock Output Signal (DIVSCLK)
An optional clock output,
DIVSCLK
, is provided which can be used as a clock source to an external
device but bears no timing relationship to other signals. Note that this signal is not synchronized to
the System Clock. By programming the
SRC
field in the
Divisor and Source Clock Configuration
(DIVSCLK)
register, the following clock outputs may be selected for
DIVSCLK
:
■ System Clock
■ PIOSC
■ MOSC
The
DIV
field in the
DIVSCLK
register controls the divided output clock frequency. The
DIVSCLK
signal is selected as an alternate function of a GPIO signal and has the same inherit electrical
characteristics of a GPIO as listed in “Electrical Characteristics” on page 1818.
System Clock Frequency
The system clock (SysClk) is the clock that is distributed to the processor and the integrated
peripherals after clock gating. The SysClk frequency is based on the frequency of the clock source
and the divisor factor. For example, if the PLL is not being used and the device is not in deep sleep
mode, then the
OSYSDIV
bit field in the
RSCLKCFG
register is the divisor used to determine the
system clock. If the PLL is being used, then
PSYSDIV
bit field in the
RSCLKCFG
register must be
programmed as well as the values in the
PLLFREQ0
and
PLLFREQ1
registers. If the device is in
deep sleep mode, then the
Deep Sleep Clock Configuration Register (DSCLKCFG)
can be
programmed with the divisor bit field
DSSYSYDIV
to modify the clock source frequency. Table
5-5 on page 235 shows the different system clock frequency calculations based on the operation
mode, clock source and PLL encoding.
Table 5-5. System Clock Frequency
Divisor Factors Used
SYSCLK Value
USEPLL
(RSCLKCFG)
Clock Mode
PSYSDIV
bit field in
RSCLKCFG
;
MINT
,
MDIV
in
PLLFREQ0
;
Q
,
N
bits in
PLLFREQ1
f
VCO
/(P 1)
1
Run or Sleep
OSYSDIV
bit field in
RSCLKCFG
f
OSCCLK
/(O 1)
0
Run or Sleep
DSSYSDIV
bit field in
DSCLKCFG
f
OSCCLK
/(DS 1)
PLL not enabled in Deep
Sleep
Deep Sleep
235
June 18, 2014
Texas Instruments-Production Data
Tiva
™
TM4C1294NCPDT Microcontroller