Peripheral Clocking
129
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Device Clocking
6.3.7 I/O Domains
The I/O domains refer to the frequencies of the peripherals that communicate through device pins. In
many cases, there are frequency requirements for a peripheral pin interface that are set by an outside
standard and must be met. It is not necessarily possible to obtain these frequencies from the on-chip clock
generation circuitry, so the frequencies must be obtained from external sources and are asynchronous to
the CPU frequency by definition.
The peripherals can be divided into the following groups, depending upon their clock requirements, as
shown in
Table 6-9. Peripherals
Peripheral Group
Peripheral Group Definition
Peripherals
Contained
within Group
Source of Peripheral Clock
RTC
Operates off of a dedicated 32 kHz
crystal oscillator.
RTC
—
Fixed-Frequency Peripherals
As the name suggests, fixed-
frequency peripherals have a fixed-
frequency. They are fed the
AUXCLK directly from the oscillator
input.
Timer64P0/P1
—
I2C0
—
Synchronous Peripherals
Synchronous peripherals have their
frequencies derived from the ARM
clock frequency. The peripheral
system clock frequency changes
accordingly, if the PLL0 frequency
changes. Most synchronous
peripherals have internal dividers
so they can generate their required
clock frequencies.
MMC/SDs
PLL0_SYSCLK2
HPI
PLL0_SYSCLK2
UART0
PLL0_SYSCLK2
LCDC
PLL0_SYSCLK2
GPIO
PLL0_SYSCLK4
Asynchronous Peripherals
Asynchronous peripherals are not
required to operate at a fixed ratio
of the ARM clock.
eCAPs
ASYNC3
eHRPWMs
ASYNC3
UART1/2
ASYNC3
Timer64P2/P3
ASYNC3
EMIFA
DIV_4P5 or PLL0_SYSCLK3
SATA
Peripheral Serial Clock
DDR2/mDDR
PLL1_SYSCLK1 or
PLL1 Direct Output
Synchronous/Asynchronous
Peripherals
Synchronous/asynchronous
peripherals can be run with either
internally generated synchronous
clocks, or externally generated
asynchronous clocks.
McASP0
ASYNC3 or
Peripheral Serial Clock
McBSPs
ASYNC3 or
Peripheral Serial Clock
SPI0
PLL0_SYSCLK2 or
Peripheral Serial Clock
SPI1
ASYNC3 or
Peripheral Serial Clock
I2C1
PLL0_SYSCLK4 or
Peripheral Serial Clock
EMAC
PLL0_SYSCLK4 or
RMII_MHZ_50_CLK
uPP
PLL0_SYSCLK2 or
Peripheral Serial Clock
VPIF
PLL0_SYSCLK2 or
Peripheral Serial Clock
USBs
USB_REFCLKIN or AUXCLK