DM74AS257M

Overview

The DM74AS257M is a discontinued 3-STATE Quad 1 of 2 Line Data Selector/Multiplexer manufactured by onsemi. It operates within a supply voltage range of 4.5V to 5.5V and supports an operating temperature range of 0°C to +70°C. The device features four independent multiplexers with true data outputs, housed in a 16-Lead Small Outline Integrated Circuit (SOIC) package. Electrical characteristics include a HIGH Level Output Current of -15 mA and a LOW Level Output Current of 48 mA.

Feature Summary

• Contains inverters and drivers for full on-chip data selection to four 3-STATE outputs.
• Interfaces directly with data lines of bus-organized systems.
• Utilizes advanced oxide-isolated, ion-implanted Schottky TTL process.
• Functionally and pin-for-pin compatible with Schottky, low power Schottky, and advanced low power Schottky TTL counterparts.

Applications

• Implementing n-bit paralleled data selectors with up to 300 sources for data buses.
• Multiplexing dual data buses.
• Routing a 4-bit word selected from one of two sources to four outputs.
• General four functions of two variables where one variable is common.

Procurement Notes

Verify component obsolescence status as the DM74AS257M is marked as obsolete and no longer manufactured. Confirm availability of equivalent replacement parts such as the SN74AS257D from Texas Instruments. Ensure that any substitute components meet the required SOIC-16 package dimensions and electrical specifications for the intended application environment.

Selection Notes

Select this component only if legacy compatibility with Fairchild Semiconductor logic families is required. Consider the specific 3-STATE output drive capability for direct bus interfacing. Evaluate the propagation delay times under specific load conditions (CL = 50 pF, RL = 500Ω) to ensure timing requirements are met. Verify that the single power supply requirement aligns with system design constraints.

Part Context

This part belongs to the 74AS series of logic integrated circuits, specifically designed for high-speed applications using Advanced Schottky technology. The DM74AS257M provides true data outputs, distinguishing it from the DM74AS258 which provides inverted data. Both devices share identical pinouts and functional characteristics, differing primarily in output polarity to optimize propagation delay performance in specific circuit configurations.

Replacement Considerations

The SN74AS257D from Texas Instruments is documented as a parameter-equivalent replacement. Verify pinout compatibility and electrical specifications before substitution.

FAQ

What is the difference between the DM74AS257 and DM74AS258?

The DM74AS257 presents true data to the outputs, whereas the DM74AS258 presents inverted data. They are functionally and pin-for-pin compatible otherwise.

Can the DM74AS257M interface directly with bus lines?

Yes, the device contains drivers to supply full on-chip data selection to the four 3-STATE outputs, allowing them to interface directly with data lines of bus-organized systems.