7:1 Serialization in Spartan-3E/3A FPGAs at Speeds Up to 666 Mbps Application Note (XAPP486) - This application note targets Spartan-3E devices in applications that require 4-bit or 5-bit transmit data bus widths and operate at rates up to 666 Mbps per line with a forwarded clock at 1/7th the bit rate.