Logic device/transceiver/encoder

The MC74VHCT257A is an advanced high-speed CMOS quad 2-channel multiplexer fabricated on a silicon-gate CMOS process. It achieves high-speed operation similar to an equivalent bipolar Schottky TTL while maintaining the low power consumption of CMOS. It consists of four 2-input digital multiplexers with common select (S) and enable (OE) bar inputs. When the (OE)bar is held high, data selection is disabled and all outputs go low. Selecting the decode determines whether the A or B input is routed to the corresponding Y output. The VHCT input is compatible with TTL levels. This device can be used as a level shifter to interface with 3.3 V to 5.0 V circuits because it has a full 5-V CMOS level output swing. The VHCT257A input structure provides protection when 0 - 5.5 V is applied regardless of the supply voltage. The output structure also provides protection when VCC = 0V. These input and output structures help prevent device damage due to supply voltage - input/output voltage mismatch, battery backup, hot insertion, etc. This internal circuit consists of three stages, including a buffer output that provides high noise immunity and stable output. The input is tolerant to 7 V and supports interfacing from 5 V systems to 3 V systems.