DM74ALS646NT

Overview

The DM74ALS646NT is an octal 3-STATE bus transceiver and register manufactured by onsemi. It features a 24-Lead Plastic Dual-In-Line Package (PDIP). The device operates within a supply voltage range of 4.5V to 5.5V and supports a clock frequency up to 40 MHz. Propagation delays from the A or B buses to outputs range from 3ns to 12ns, while delays from control inputs like SAB/SBA range from 5ns to 35ns. Output drive capabilities include a low-level current of 24mA and a high-level current of -15mA.

Feature Summary

• Incorporates independent D-type registers for both Bus A and Bus B to store data internally.
• Features multiplexed transmission capability allowing selection between real-time bus data and stored register data.
• Utilizes totem-pole 3-STATE outputs designed to drive highly-capacitive loads directly without interface components.

Applications

• Implementing buffer registers in bus-organized systems
• Creating bidirectional bus drivers for data transfer between buses
• Designing I/O ports with storage capabilities
• Functioning as working registers in digital logic circuits

Procurement Notes

Verify the package type matches the specific suffix; 'NT' indicates a 24-lead PDIP. Confirm that the application environment stays within the recommended operating temperature range of 0°C to +70°C. Ensure power supply voltages do not exceed the maximum ratings to prevent damage. Check for any specific ordering suffix requirements if tape and reel packaging is needed instead of tube.

Selection Notes

Select this component when an octal transceiver with integrated storage is required for bidirectional data flow. It is suitable for applications needing direct bus driving without pull-up resistors. Consider the propagation delay specifications relative to system timing requirements. Verify that the 3-STATE output characteristics meet the load impedance needs of the target bus architecture.

Part Context

This part belongs to the 74ALS series of logic devices, utilizing advanced oxide-isolated, ion-implanted Schottky TTL process technology. It is functionally compatible with other standard 74ALS octal bus transceivers but includes unique dual-register storage features controlled by separate clock inputs for each bus direction.

Replacement Considerations

Check datasheets for equivalent parts offering similar octal 3-STATE functionality with dual registers. Verify pinout compatibility and electrical parameters such as propagation delay and output drive current before substitution.

FAQ

How does the device handle data transitions between stored and real-time modes?

The select controls (SAB and SBA) utilize a make-before-break configuration to eliminate glitches that typically occur during transitions between storing data and passing real-time bus data.

What is the function of the enable G and direction control pins?

These pins provide four modes of operation: real-time transfer from bus A to B, real-time transfer from bus B to A, transferring bus data to internal storage, or transferring stored data back to the buses.