SN74AS138

The ALS138A and AS138 are 3-line to 8-line decoders/demultiplexers designed for highperformance memory-decoding or data-routing applications requiring very short propagation delay times. In high-performance systems, these SN74AS138 devices can be used to minimize the effects of system decoding. When employed with high-speed memories with a fast enable circuit, the delay times of the decoder and the enable time of the memory are usually less than the typical access time of the memory. The effective system delay introduced by the Schottky-clamped system
decoder is negligible.

The SN74AS138 conditions at the binary-select (A, B, and C) inputs and the three enable (G1, G2A, and G2B) inputs select one of eight output lines. Two active-low and one active-high enable inputs reduce the need for external gates or inverters when expanding. A 24-line decoder can be implemented without external inverters and a 32-line decoder requires only one inverter. An enable input can be used as a data input for demultiplexing applications.

The SN54ALS138A and SN54AS138 are characterized for operation over the full military temperature range of 55°C to 125°C. The SN74ALS138A and SN74AS138 are characterized for operation from 0°C to 70°C.