The HC139 and HCT139 devices contain two independent binary to one of four decoders each with a single active low enable input (1E\ or 2E\). Data on the select inputs (1A0 and 1A1 or 2A0 and 2A1) cause one of the four normally high outputs to go low.
If the enable input is high all four outputs remain high. For demultiplexer operation the enable input is the data input. The enable input also functions as a chip select when these devices are cascaded. This device is functionally the same as the CD4556B and is pin compatible with it.
The outputs of these devices can drive 10 low power Schottky TTL equivalent loads. The HCT logic family is functionally as well as pin equivalent to the LS logic family.