74HCT259

The 74HCT259 is high-speed Si-gate CMOS devices and are pin compatible with low power Schottky TTL (LSTTL). They are specified in compliance with JEDEC standard no. 7A.

The 74HCT259 is  high-speed 8-bit addressable latches designed for general purpose storage applications in digital systems. The "259" are multifunctional devices capable of storing single-line data in eight addressable latches, and also 3-to-8 decoder and demultiplexer, with active HIGH outputs (Q₀ to Q₇), functions are available.

The "259" also incorporates an active LOW common reset (MR) for resetting all latches, as well as, an active LOW enable input (LE).

The "259" has four modes of operation as shown in the mode select table. In the addressable latch mode, data on the data line (D) is written into the addressed latch. The addressed latch will follow the data input with all non-addressed latches remaining in their previous states. In the memory mode, all latches remain in their previous states and are unaffected by the data or address inputs.

In the 3-to-8 decoding or demultiplexing mode of the 74HCT259, the addressed output follows the state of the D input with all other outputs in the LOW state. In the reset mode all outputs are LOW and unaffected by the address (A₀ to A₂) and data (D) input. When operating the "259" as an addressable latch, changing more than one bit of address could impose a transient-wrong address. Therefore, this should only be done while in the memory mode. The mode select table summarizes the operations of the "259".