How do you implement GTLP Input support in Spartan-3A or Spartan-6 devices?
Spartan-3A and Spartan-6 devices use differential buffers for HSTL and SSTL input levels. Differential input buffers can be made compatible with GTLP switching levels by modifying the termination scheme, and adjusting VREF and VTT as per GTLP requirements.
1. Select the HSTL_I or HSTL_III input buffer.
2. Connect VREF to 1.0V.
NOTE: GTLP support in Spartan-3A and Spartan-6 devices is limited to Input Only.