XEM8305
Clock Oscillators
Note: The clock oscillators are separate and not synchronous to the clock provided by the USB host interface.
In addition to the USB host interface clock, one fixed-frequency clock oscillator provides a reference clock for various FPGA components and systems.
- Fabric / DDR4 Clock – This is a general-purpose 156.25 MHz LVDS clock for logic use. This clock should be used as the reference for designs using the DDR4 memory. This clock is using an SiTime SiT9375AI-02A2-1810-156.250000 or equivalent component.
There is one 6 pin, 3.2mm x 2.5mm, 1.8V VCC, LVDS output oscillator footprint available on the board that is not normally placed. This oscillator is connected to the MGT quad 225 refclock 1 input. It is designator U2 on the PCB. An example compatible component is the Skyworks 511JBA125M000CAGR.
Refclock 0 for the three MGT quads (banks 224, 225, and 226) are also brought out to the expansion connectors. See the Pins List for connection details.
Pin Mappings
| CLOCK | Designator | FREQUENCY | FPGA PINS (P / N) | I/O Standard |
|---|---|---|---|---|
| Fabric / DDR4 | U12 or U3 | 156.25 MHz | J23 / J24 (Bank 66) | LVDS |
| MGT 225 Refclk 1 | U2 | Not Placed | T7 / T6 (Bank 225) | LVDS |
| MGT 224 Refclk 0 | External (MC3) | AB7 / AB6 (Bank 224) | LVDS | |
| MGT 225 Refclk 0 | External (MC3) | V7 / V6 (Bank 225) | LVDS | |
| MGT 226 Refclk 0 | External (MC2) | P7 / P6 (Bank 226) | LVDS |