The Simultaneous Switching Output (SSO) guidelines for Virtex-E and Virtex-II omit entries for LVDS and LVPECL. What is the recommended maximum number of SSOs for these signals?
For SSO guidelines, use these substitutions:
Virtex-E, LVDS: one output pair = one LVTTL 2mA driver with fast slew rate
Virtex-E, LVPECL: one output pair = one LVTTL 24mA driver with fast slew rate
The Virtex-II/Pro LVPECL driver is identical to the Virtex-E driver.
Because the Virtex-II LVDS driver is very balanced, its switching causes a negligible amount of transient current. As a result, SSOs are not a problem. For more information, please see (Xilinx Answer 12629).
The Virtex-E SSO guidelines are provided in the Virtex-E data sheet at:
Select "Detailed Functional Description" -> "Using SelectI/O" -> "Design Considerations" -> "Simultaneous Switching Guidelines".
The Virtex-II SSO guidelines are provided in the "Virtex-II Platform FPGA User Guide" at:
Select "Design Considerations" -> "Using Single-Ended Select I/O Ultra Resources" -> "Design Considerations" -> "SSO Guidelines".