DM74AS640WMX

Overview

The DM74AS640WMX is a 3-State Octal Bus Transceiver manufactured by onsemi, utilizing an advanced oxide-isolated, ion-implanted Schottky TTL process. It contains eight pairs of logic elements configured for asynchronous bidirectional data buses. The device transmits data between A and B buses based on the DIR input level, while the G input enables or disables the outputs for bus isolation. It features protection against bus glitching during power-up or power-down and is designed to drive terminated transmission lines with low output impedance.

Feature Summary

• 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
• Improved AC performance over standard Schottky and Low Power Schottky variants
• Independent 3-State control on A and B buses with power-up/down glitch prevention

Applications

• Memory systems
• Microprocessor systems
• Asynchronous bidirectional data buses

Procurement Notes

Verify component authenticity through authorized channels as this part originates from Fairchild Semiconductor, now part of onsemi. Confirm package integrity and check for RoHS compliance status specific to manufacturing dates. Ensure the ordering code suffix 'X' matches the required tape and reel packaging format. Validate that the SOIC-20 package dimensions align with your PCB footprint requirements before finalizing procurement.

Selection Notes

Select this component when high-speed bidirectional data transfer is required in memory or microprocessor architectures. It serves as a direct replacement for older Schottky and Low Power Schottky octal bus transceivers due to its pin compatibility. Consider its improved AC performance and low output impedance for driving terminated transmission lines up to 133 ohms. Ensure system voltage ranges between 4.5V and 5.5V and operating temperatures fall within 0°C to +70°C.

Part Context

This device belongs to the 74AS series of logic integrated circuits, characterized by advanced Schottky technology for high-speed operation. It is functionally equivalent to other octal bus transceivers in the 74ALS and 74S families but offers superior switching speeds. The DM74AS640 is housed in a 20-Lead Small Outline Integrated Circuit (SOIC) package, designated as M20B, suitable for surface-mount applications requiring compact board space.

Replacement Considerations

SN74AS640NSR Texas Instruments

FAQ

How does the device handle bus isolation?

Bus isolation is achieved by setting the enable input (G) to a HIGH logic level, which disables the outputs and effectively isolates buses A and B.

What is the maximum propagation delay time?

The maximum propagation delay time from A or B to B or A is 7 ns for LOW-to-HIGH transitions and 6 ns for HIGH-to-LOW transitions under specified conditions.

Can this device interface with CMOS logic?

Yes, the device is specified to interface with CMOS logic at V_OH = V_CC - 2V.