
clock inputs and SYSCLK is unused. Power-on-configuration signal cfg_eng_use0
selects between SYSCLK (single ended) and DIFF_SYSCLK/DIFF_SYSCLK_B
(differential) clock inputs.
2. In the "Single Oscillator Source" reference clock mode, DIFF_SYSCLK/
DIFF_SYSCLK_B clock inputs can be selected to feed the DDR PLL. RCW bits
[DDR_REFCLK_SEL] are used for this selection and DDRCLK is unused. The
options for RCW bits 186-187 are as follows:
a. RCW[DDR_REFCLK_SEL]=00; The DDRCLK pin provides the reference
clock to the DDR PLL
b. RCW[DDR_REFCLK_SEL]=01; DIFF_SYSCLK/DIFF_SYSCLK_B
provides the reference clock to the DDR PLL
3. When SYSCLK is chosen as the primary clock input to the chip, these pins are
unused.
4. Either of the EC1_GTX_CLK125 or EC2_GTX_CLK125 can be used to clock
both the EC interfaces in RGMII mode. The selection can be made through
SCFG_ECGTXCMCR[CLKSEL].
5.30 Single source clocking
The chip supports the single source clocking options with single, two, and more reference clocks.
5.31 Single oscillator source reference clock mode
In this mode, single onboard oscillator can provide the reference clock (100 MHz) to the following PLLs:
• Platform PLL
• Core PLLs
• USB PLL
• DDR PLL
• SerDes PLLs
The reset configuration field identifies whether the SYSCLK (single-ended) or DIFF_SYSCLK (differential) is selected as
the clock input to the chip.
The RCW[DDR_REFCLK_SEL] bit is used to select clock input (DIFF_SYSCLK or DDRCLK) to the DDR PLL.
The following figure shows the system view of single oscillator source clocking. In this figure, the on-board oscillator
generates three differential clock outputs. The first differential output is used to provide the clock to system clock associated
PLLs and DDR PLL. However, the second and third differential outputs are used to provide clocks to SerDes PLLs.
A multiplexer between SYSCLK and DIFF_SYSCLK/DIFF_SYSCLK_B is used to provide the USB PHY reference clock to
the USB PLL. And, multiplexer between DIFF_SYSCLK/DIFF_SYSCLK_B inputs and DDRCLK is used to provide
reference clock to the DDR PLL.
The duty cycle reshaper reshapes the 125 MHz ECn_GTX_CLK125 which is fed into frame manager for transmission as
ECn_GTX_CLK.
Interface recommendations
QorIQ LS1046A Design Checklist , Rev. 2, 06/2020
NXP Semiconductors
49