Texas Instruments SN74ALS1245AN

Overview

SN74ALS1245AN from Texas Instruments is an octal bidirectional bus transceiver with 3-state outputs in a 20-pin PDIP package, operating from 0°C to 70°C at 4.5–5.5 V supply. It enables asynchronous A↔B data flow controlled by DIR and isolates buses via OE, supporting TTL-compatible logic levels and driving up to 16 mA low-level output current. It is used in legacy industrial backplane and microprocessor system bus interfacing.

For engineers reviewing the SN74ALS1245AN datasheet, SN74ALS1245AN pinout, SN74ALS1245AN application, or SN74ALS1245AN equivalent, key selection criteria include its 3-state bidirectional control architecture, 13 ns max propagation delay (A→B/B→A), 25 mA max ICC in disabled state, and compatibility with standard 5-V TTL bus loading requirements.

Technical Context

The SN74ALS1245AN implements dual 8-bit bidirectional data paths using complementary TTL circuitry with active-low 3-state enable (OE) and unidirectional direction control (DIR). Its internal structure supports simultaneous high-impedance isolation of both A and B ports when OE is high, independent of DIR state.

It features ALS-family characteristics: lower power than standard TTL (max 40 mA ICC disabled), improved noise margin (VIL = 0.8 V, VIH = 2 V), and guaranteed switching performance across full commercial temperature range with CL = 50 pF load.

Key Specifications

Pinout & Package

SN74ALS1245AN uses a 20-pin plastic dual in-line package (PDIP-N), 300-mil width, with 0.1-inch lead pitch and through-hole mounting. Package dimensions: 506 mm × 13.97 mm × 11.23 mm (L×W×H).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar bidirectional bus transceiver applications.

Compared with SN74LS245N and SN74HC245N, the SN74ALS1245AN delivers optimal balance of TTL compatibility, 13 ns speed, and 40 mA disabled ICC-making it the precise choice for upgrading LS-based systems without redesigning power or interface layers.

Availability

SN74ALS1245AN is available at Aetrix Electronics and suitable for microprocessor bus extension, industrial backplane interfacing, test equipment data acquisition, and embedded instrumentation front-end designs requiring stable component supply and long-term obsolescence management.

Supply support for SN74ALS1245AN 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 global semiconductor leader founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN74ALS1245AN belongs to TI's legacy ALS (Advanced Low-Power Schottky) logic family, engineered for high-speed, low-power 5-V TTL system interfacing in the 1980s–1990s-still widely deployed in maintenance-critical industrial infrastructure.

FAQ

What is the maximum operating frequency supported by the SN74ALS1245AN?

The SN74ALS1245AN does not specify a maximum clock frequency in its datasheet because it is an asynchronous transceiver. However, its 13 ns maximum propagation delay (tPLH/tPHL) and 3 ns minimum disable time (tPLZ) support reliable operation in 20–30 MHz bus systems when paired with appropriate setup/hold timing margins. The actual usable frequency depends on system-level trace length, loading, and controller timing constraints-not an internal clock.

Can the SN74ALS1245AN be used with 3.3-V logic systems?

No-the SN74ALS1245AN is strictly a 5-V TTL device with VIH = 2.0 V min and VIL = 0.8 V max, and it requires VCC = 4.5–5.5 V. Its outputs swing near 0 V and 3.4 V (VOH min at –15 mA), which may not meet 3.3-V logic high thresholds reliably. For 3.3-V systems, use a level-shifting transceiver such as the TXB0108 instead of the SN74ALS1245AN.

Is the SN74ALS1245AN pin-compatible with the SN74LS245N?

Yes-the SN74ALS1245AN and SN74LS245N share identical 20-pin PDIP (N) package pinout, DIR/OE control logic, and A/B port mapping. This allows direct physical replacement in existing PCBs. However, designers must verify that the reduced ICC and faster timing of the SN74ALS1245AN do not cause unintended signal integrity or timing violations in legacy LS-based layouts.

What is the purpose of the DIR and OE pins on the SN74ALS1245AN?

The DIR (direction) pin controls data flow direction: DIR = low enables B→A transfer; DIR = high enables A→B transfer. The OE (output enable, active-low) pin controls 3-state output drivers: OE = high places all A and B pins in high-impedance isolation; OE = low activates the selected direction path. Both signals operate independently-OE overrides DIR when disabled.

Does the SN74ALS1245AN require external pull-up resistors on its I/O pins?

No-external pull-ups are not required. The SN74ALS1245AN has active push-pull outputs capable of sourcing –15 mA and sinking 16 mA, fully compliant with standard TTL loading. Pull-ups would interfere with bidirectional operation and violate the device's 3-state control architecture. Only decoupling capacitors (0.1 µF at VCC) are mandatory per TI recommendations for the SN74ALS1245AN.