Programmable QSFP4 Clock
, callout 16]
The VCU128 evaluation board has a SI570 I2C programmable low-jitter 3.3V LVDS differential
oscillator (U80) connected to FPGA U1 GTY bank 131 MGTREFCLK0 P/N pins AB42 and AB43
(series capacitor coupled), respectively.
On power-up, the U80 SI570 user clock defaults to an output frequency of 156.250 MHz. The
Zynq-7000 SoC system controller or FPGA implemented user IP can change the output
frequency within the range of 10 MHz to 810 MHz through an I2C interface. Power cycling the
VCU128 evaluation board resets the QSFP4 clock to the default frequency of 156.250 MHz
• Programmable oscillator: Silicon Labs Si570BAB0000544DG (10 MHz-810 MHz)
• Frequency tolerance: 50 ppm
• 3.3V LVDS differential output
The programmable QSFP4 clock circuit is shown in the following figure.
Figure 16: QSFP4 Clock
X21966-121918
Chapter 3: Board Component Descriptions
UG1302 (v1.1) April 21, 2021
VCU128 Board User Guide
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