Texas Instruments SN74ALS648ANT

Overview

SN74ALS648ANT from Texas Instruments is an octal bus transceiver and register IC with 3-state inverting outputs, designed for bidirectional data flow control between two 8-bit buses (A and B). It features independent A/B registers, real-time or stored data multiplexing via SAB/SBA controls, DIR-controlled directionality, and OE-gated 3-state output enable. It operates at up to 40 MHz clock frequency with 5 V supply and is used in legacy industrial backplane and memory-mapped I/O systems requiring registered bus isolation.

For engineers reviewing the SN74ALS648ANT datasheet, SN74ALS648ANT pinout, SN74ALS648ANT application, or SN74ALS648ANT equivalent, key selection criteria include its inverting logic path, dual-register storage capability, CLKAB/CLKBA edge-triggered latching, 3-state output drive strength (24 mA sink), and compatibility with standard 24-pin plastic DIP (NT) packaging for through-hole prototyping and repair.

Technical Context

This device integrates eight identical channels, each containing D-type flip-flops for A- and B-bus data registration, combinational transceiver logic, and 3-state output drivers. Data is latched on the low-to-high transition of CLKAB (A→B) or CLKBA (B→A), while DIR selects active bus direction and OE enables/disables outputs without affecting input functionality.

The select-control inputs SAB and SBA eliminate decoding glitches during transitions between real-time (transparent) and stored data modes. The SN74ALS648ANT implements inverting data paths - output data is logically inverted relative to input - distinguishing it from the non-inverting SN74ALS646A and higher-speed SN74AS648 variants.

Key Specifications

Pinout & Package

SN74ALS648ANT uses a 24-pin plastic dual in-line package (NT), 300-mil width, with standard through-hole footprint. Pin 1 is top-left corner when notch faces up; pin numbering follows counter-clockwise convention.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal registered transceiver applications.

Compared with SN74ALS648A and SN74AS648, the SN74ALS648ANT provides verified through-hole compatibility, lower power consumption, and sufficient timing margin for legacy 40 MHz bus systems - making it the optimal choice for repair, refurbishment, and cost-sensitive prototyping where SOIC rework or AS-family noise sensitivity is prohibitive.

Availability

SN74ALS648ANT is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy memory-mapped I/O subsystems, and test equipment bus controllers requiring stable component supply and long-term obsolescence mitigation.

Supply support for SN74ALS648ANT includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic ICs with broad industrial and automotive qualification.

The SN74ALS648ANT belongs to TI's legacy ALS (Advanced Low-Power Schottky) logic family, engineered for reliable 5 V TTL-compatible operation in cost-sensitive, medium-speed digital systems where power efficiency and noise immunity were prioritized over maximum speed.

FAQ

What is the logic polarity of SN74ALS648ANT outputs?

The SN74ALS648ANT implements an inverting data path: output data on either A or B bus is logically inverted relative to the corresponding input. This distinguishes it from the non-inverting SN74ALS646A and is explicitly confirmed in the device description and function tables of the SDAS039F datasheet. The inversion applies to both real-time and stored data modes.

Does SN74ALS648ANT support 3.3 V operation?

No, SN74ALS648ANT is strictly a 5 V device. Its recommended operating voltage is 4.5 V to 5.5 V, and absolute maximum VCC is 7 V. It lacks 3.3 V logic-level compatibility - applying 3.3 V to VCC will result in undefined operation, insufficient noise margin, and potential failure to meet timing specifications. Use level translators if interfacing with 3.3 V systems.

Can SN74ALS648ANT replace SN74ALS648A in a design?

Yes, SN74ALS648ANT is a direct functional and pinout-compatible replacement for SN74ALS648A in through-hole applications, as both share identical logic behavior, DC specs, and 24-pin NT package. However, SN74ALS648A is only offered in SOIC (DW) packaging - so SN74ALS648ANT serves as the sole through-hole option for this function within the ALS648 family.

What is the purpose of the NC pins on SN74ALS648ANT?

SN74ALS648ANT has three NC (No internal connection) pins: pins 12 (GND), 21 (OE), and 22 (SBA) are *not* NC - correction: per the pin diagram, pins labeled "NC" in the top-view drawing (e.g., pins adjacent to CLKAB, SAB, DIR, and VCC) have no internal bond wire or circuit connection. These pins must remain unconnected; routing traces or soldering to them may cause mechanical stress or unintended coupling but will not affect functionality.

How does the SN74ALS648ANT handle simultaneous A and B bus storage?

The SN74ALS648ANT supports concurrent storage: asserting both CLKAB↑ and CLKBA↑ in the same cycle latches data from A bus into the B-register *and* from B bus into the A-register simultaneously. This is confirmed in the Function Tables (page 3), where "Store A and B data" is enabled when OE = H and clocks are active - enabling true bidirectional snapshot capture without sequential overhead.