DM74ALS645AWM

Overview

The DM74ALS645AWM is an octal bus transceiver from the Advanced Low-power Schottky (ALS) logic family, manufactured by Fairchild Semiconductor. It features eight bidirectional data paths with non-inverting outputs and three-state capability. The device operates within a standard voltage range of 4.5V to 5.5V and supports asynchronous two-way communication between data buses. Direction control is managed via a DIR input, while an output-enable input isolates the buses when disabled. It is housed in a 20-pin Small Outline Integrated Circuit (SOIC) package.

Feature Summary

• Provides bidirectional data transmission between two independent buses using a single direction control input.
• Features three-state outputs that enter high-impedance mode when disabled, effectively isolating connected buses.
• Utilizes Advanced Low-power Schottky technology for improved switching speed and reduced power consumption compared to standard LS logic.

Applications

• Asynchronous two-way communication between data buses in microprocessor systems
• Memory interface circuits requiring bidirectional data transfer
• General-purpose bus drivers in digital logic designs

Procurement Notes

Verify the manufacturer origin, as this component is produced by multiple entities including Fairchild, ON Semiconductor, Texas Instruments, and Rochester Electronics under identical part numbers. Confirm the specific suffix or marking if strict lineage is required. Ensure the SOIC-20 package matches the design footprint. Check for lead-free compliance markings if environmental regulations apply to the assembly process.

Selection Notes

Select this component when non-inverting octal bus transceivers are required for ALS-speed applications. It serves as a functional equivalent to other octal transceivers but offers lower power dissipation than standard TTL families. Consider the three-state isolation feature for bus arbitration. Verify that the operating temperature range of 0°C to 70°C meets the system requirements, as military-grade variants exist with different suffixes.

Part Context

This device belongs to the SN74ALS645A series, widely used in legacy and industrial digital systems. It is functionally compatible with similar octal transceivers like the DM74ALS245AWM, though the latter provides true (non-inverted) outputs. The ALS family bridges the performance gap between standard LS and AS logic, offering faster propagation delays with moderate power usage.

Replacement Considerations

Direct substitutes include DM74ALS245AWM for non-inverting applications, though output polarity differs. Cross-family replacements such as SN74LS245 or SN74HC245 may fit electrically but differ in speed and drive strength. Verify pinout compatibility before substituting with generic octal bus transceivers.