An I/O standard used for high-speed I/O interfaces, the Differential SSTL-2 I/O standard uses differential inputs without a reference voltage.

An I/O standard with a termination (V_TT) voltage of 0.9 V, an output (V_CCIO) voltage of 2.5 V, a GTL+/SSTL input buffer and a 3.3-V/2.5-V TTL output buffer. The Differential SSTL-2 I/O standard is supported by the Stratix^™ and Stratix^™ GX device families.