![Texas Instruments AM1808 Technical Reference Manual Download Page 117](http://html.mh-extra.com/html/texas-instruments/am1808/am1808_technical-reference-manual_1094558117.webp)
Overview
117
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Device Clocking
6.1
Overview
This device requires two primary reference clocks:
•
One reference clock is required for the phase-locked loop controllers (PLLCs)
•
One reference clock is required for the real-time clock (RTC) module.
These reference clocks may be sourced from either the on-board oscillator via an externally supplied
crystal or by a direct external oscillator input. For detailed specifications on clock frequency and voltage
requirements, see the electrical specifications in your device-specific data manual.
In addition to the reference clocks required for the PLLCs and RTC module, some peripherals, such as the
USB, may also require an input reference clock to be supplied. All possible input clocks are described in
. The CPU and the majority of the device peripherals operate at fixed ratios of the primary
system/ARM clock frequency, as listed in
. However, there are two system clock domains that do
not require a fixed ratio to the ARM, these are PLL0_SYSCLK3 and PLL0_SYSCLK7.
shows
the clocking architecture.
Table 6-1. Device Clock Inputs
Peripheral
Input Clock Signal Name
Oscillator/PLL
OSCIN
RTC
RTC_XI
JTAG
TCK, RTCK
EMAC RMII
RMII_MHZ_50_CLK
EMAC MII
MII_TXCLK, MII_RXCLK
USB2.0 and USB1.1
USB_REFCLKIN
I2Cs
I2Cn_SCL
Timers
TM64Pn_IN12
SATA
SATA_REFCLKP, SATA_REFCLKN
SPIs
SPIn_CLK
uPP
UPP_CHn_CLK
VPIF
VPIF_CLKINn
McBSPs
CLKSn, CLKRn, CLKXn
McASP0
ACLKR, AHCLKR, ACLKX, AHCLKX
Table 6-2. System Clock Domains
CPU/Device Peripherals
System Clock Domain
Fixed Ratio to
ARM Clock Required?
Default Ratio to
ARM Clock
ARM RAM/ROM, On-chip RAM, UART0, EDMA, SPI0,
MMC/SDs, VPIF, LCDC, SATA, uPP, DDR2/mDDR
(bus ports), USB2.0, HPI, PRU subsystem
PLL0_SYSCLK2
Yes
1:2
EMIFA
PLL0_SYSCLK3
No
1:3
System configuration (SYSCFG), GPIO, PLLCs, PSCs,
I2C1, EMAC/MDIO, USB1.1, ARM INTC
PLL0_SYSCLK4
Yes
1:4
ARM
PLL0_SYSCLK6
Yes
1:1
EMAC RMII clock
PLL0_SYSCLK7
No
1:6
I2C0, Timer64P0/P1, RTC, USB2.0 PHY, McASP0
serial clock
PLL0_AUXCLK
Not Applicable
Not Applicable
DDR2/mDDR PHY
PLL1_SYSCLK1
Not Applicable
Not Applicable
PLL0 input reference clock
(not configured by default)
PLL1_SYSCLK3
Not Applicable
Not Applicable
ECAPs, UART1/2, Timer64P2/3, eHRPWMs, McBSPs,
McASP0, SPI1
ASYNC3
Not Applicable
Not Applicable