Texas Instruments SN74ALS232BN

Overview

SN74ALS232BN from Texas Instruments is a 16 × 4 asynchronous first-in, first-out (FIFO) memory IC with independent write/read clocks (LDCK/UNCK), 40 MHz maximum clock frequency, 14 ns typical fall-through time, 3-state outputs, and full/empty status flags. It serves as a data buffering interface between mismatched-speed digital subsystems in communication controllers and protocol bridges.

For engineers reviewing the SN74ALS232BN datasheet, SN74ALS232BN pinout, SN74ALS232BN application, or SN74ALS232BN equivalent, this device supports high-speed parallel word-level FIFO buffering with deterministic latency, noninverting data path, and reset-controlled pointer initialization - critical for synchronous-to-asynchronous domain bridging in legacy industrial and telecom interfaces.

Technical Context

The SN74ALS232BN implements a dual-pointer ring-counter architecture with separate LDCK-triggered write address increment and UNCK-triggered read address increment. Its internal 16-word × 4-bit RAM array uses TTL-compatible ALS logic, enabling operation at 5 V with VIH = 2 V and VIL = 0.8 V.

Status monitoring relies on open-collector FULL and EMPTY flags driven by counter state comparison (CT = 0 or CT = 16), while RST asynchronously resets pointers and forces EMPTY = low / FULL = high without affecting Q output states. Output-enable (OE) controls tri-state behavior independently of status flag logic.

Key Specifications

Pinout & Package

SN74ALS232BN is supplied in a 16-pin plastic dual in-line package (PDIP-N), 300-mil width, with through-hole mounting and JEDEC-standard pinout. Thermal resistance θJA = 78°C/W enables operation at full speed without forced air in ambient ≤ 50°C.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar FIFO memory applications.

Compared with SN74ALS232BN, SN74AS232N delivers lower latency but demands stricter power integrity, while 7203L15 offers greater depth and CMOS efficiency at the cost of 4-bit alignment and reduced output drive - making SN74ALS232BN optimal for legacy 5 V TTL systems requiring exact 16×4 buffering.

Availability

SN74ALS232BN is available at Aetrix Electronics and suitable for UART interface buffering, ISA bus data bridging, and HDLC protocol controller applications requiring stable component supply across long-lifecycle industrial deployments.

Supply support for SN74ALS232BN 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 solutions with broad industrial and automotive qualification.

The SN74ALS232BN belongs to TI's legacy 74ALS logic family, designed specifically for high-speed, low-power 5 V TTL-compatible data-path buffering in commercial-grade instrumentation and communications equipment.

FAQ

What is the maximum clock frequency supported by the SN74ALS232BN?

The SN74ALS232BN supports a maximum clock frequency of 40 MHz on both LDCK and UNCK inputs under recommended operating conditions (VCC = 4.5 V to 5.5 V, TA = 0°C to 70°C). At 50% duty cycle, the practical limit is 33.3 MHz due to pulse-width constraints (LDCK high/low ≥ 10/15 ns). This rating is verified per SCAS251B timing specifications and applies to both write and read operations independently.

Does the SN74ALS232BN require external pull-up resistors on FULL and EMPTY pins?

Yes, the SN74ALS232BN features open-collector FULL and EMPTY outputs, which require external pull-up resistors to VCC (typically 4.7 kΩ) to assert high-level logic states. Without pull-ups, these flags remain floating and cannot reliably indicate non-full or non-empty conditions. The datasheet specifies VOL ≤ 0.5 V at IOL = 8 mA, confirming active-low sinking capability.

How does the RST pin affect the Q outputs of the SN74ALS232BN?

The RST pin on the SN74ALS232BN resets internal write and read pointers and forces EMPTY = low and FULL = high, but it does not alter the logic states of Q0–Q3 outputs. Those outputs retain their last valid data or float depending on OE state. The first LDCK rising edge after RST releases EMPTY = high and presents the oldest stored word on Q outputs - no data loss occurs during reset.

Can the SN74ALS232BN be cascaded to increase word width beyond 4 bits?

Yes, the SN74ALS232BN supports cascading in the word-width direction (i.e., stacking multiple devices to create 8-bit, 12-bit, or wider parallel interfaces) using shared LDCK, UNCK, RST, and OE signals while routing D0–D3 and Q0–Q3 separately. Cascading in word-depth direction (increasing from 16 to 32+ words) is not supported - the architecture lacks depth-expansion control signals or daisy-chain capability.

What is the fall-through time specification for the SN74ALS232BN, and what does it represent?

The SN74ALS232BN has a typical fall-through time of 14 ns, defined as the propagation delay from LDCK rising edge to valid Q output data. This parameter reflects the minimum latency for newly written data to become readable - critical for real-time systems where worst-case latency must be bounded. The datasheet specifies tpd = 14–23 ns (typ/max) for LDCK↑ → Q, measured at VCC = 5 V and TA = 25°C.