DM74ALS640AWM

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The DM74ALS640A is an 8-bit address latch, or register, designed by Fairchild Semiconductor. The device is designed to accept parallel input data and give parallel output, operating at high speed. It is characterized by very low power consumption, usually 250uW at a clock frequency of 20MHz.

The DM74ALS640A is classed as a buffered register, functioning as both an address latch and a data buffer. As an address latch, it can store eight address lines in parallel and provide eight outputs, each to be used by some other circuit. Those signals can be used as the address lines of a larger address space; in conjunction with a memory decoder, for example. As a data buffer, it can store bi-directional data for two lines, and both line individual output data.

The DM74ALS640A is constructed from three 8-bit latches, two dedicated for address lines and the third used for data buffering. A pair of clock inputs is used to either latch the addresses, or to read or write data from the buffering latch. All lines are TTL level compatible and provide fan-out of 12 loads. The device is offered in a PDIP package.

The DM74ALS640A has several uses. It can be used as an address latch when interfacing a processor to memory in a system or as a shift register. It can also be used in controller based systems. Additionally it is suitable for fan-out of two controllable lines for two-way data communication.

There are several basic principles that condition the way the DM74 ALS640A works. The address-latch strobe is basically a delayed strobe signal that becomes active after the address inputs have been captured and stored in the address latches. The data-strobe signal is also a delayed strobe that is enabled after the data has been placed in the data latch. Both latches will accept new data when the data-strobe or address-strobe signal is enabled. The data-strobe signal is active when the clock goes high and is reset when the clock goes low. The address-latch strobe signal is active when the address is placed on the inputs and is reset when a low signal is detected on the clock.

The signal flow of the DM74ALS640A is easy to follow. Data is first loaded into the device as parallel input from a processor. The address-latch signal is generated by the clock line and is used to latch the 8-bit address lines in the device\'s address latch. This will then provide the 8-bit address lines to the memory or other peripheral device. The data-strobe signal is set when the clock goes high, enabling the device to store the data in the data latch. The data-strobe is then reset when the clock goes low, providing the data to the peripheral device or memory.

Being an 8-bit buffered register, the DM74ALS640A provides useful functionality in a variety of applications. Its low power consumption, easy to read signal flow, and TTL level compatibility make it one of the most popular and reliable devices in the Fairchild family. Its use in controller-based systems, shift registers, and memory interfacing makes it a valuable part of any electronic system.

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