An I/O standard used for high-speed I/O interfaces, 3.3-V PCML (pseudo-current mode logic) uses differential inputs without a reference voltage and uses a differential signal with an output (V_CCIO) voltage of 3.3 V. The 3.3-V PCML I/O standard is supported by the APEX^™ II, Mercury^™, Stratix^™ and Stratix^™ GX device families.