Texas Instruments SN74F657DWR

Overview

SN74F657DWR from Texas Instruments is an octal transceiver with integrated 8-bit parity generator/checker and 3-state outputs, designed for bidirectional bus interfacing in TTL-level systems. It supports A↔B data flow direction control via T/R input, provides selectable odd/even parity via ODD/EVEN pin, and delivers 64 mA sink capability at B-port outputs - enabling robust termination in backplane and memory bus applications.

For engineers reviewing the SN74F657DWR datasheet, SN74F657DWR pinout, SN74F657DWR application, or SN74F657DWR equivalent, key selection criteria include its dual-role parity logic (generator during transmit, checker during receive), high-drive 3-state B outputs, low-input loading (70 µA), and SOIC-24 package compatibility with legacy F-series TTL bus architectures.

Technical Context

The SN74F657DWR implements a synchronous, noninverting bidirectional transceiver architecture where data direction is controlled by the T/R signal: high enables A→B transmission (PARITY output active), low enables B→A reception (PARITY input active). Its parity logic evaluates all eight A or B inputs simultaneously to generate or verify even/odd parity based on the ODD/EVEN setting.

Output enable (OE) independently places both A and B ports into high-impedance state regardless of T/R state. The ERR output asserts high only when received parity matches expected parity (e.g., even parity input with even number of high bits on B port), providing real-time error detection without external logic.

Key Specifications

Pinout & Package

SN74F657DWR is housed in a 24-pin SOIC (DW) package with 300-mil width, surface-mount compatible, and RoHS-compliant with NiPdAu lead finish. Pin 1 is located at the top-left corner (notch or dot indicator), and the device uses standard JEDEC SOIC-24 footprint (7.5 mm × 15.4 mm).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal transceiver-with-parity applications.

Compared with SN74F657DWR, SN74F245DW requires external parity circuitry and increases BOM count, while SN74LS657N sacrifices speed and drive strength for lower power - making SN74F657DWR the sole integrated, high-performance, RoHS-compliant solution for parity-critical 5 V TTL bus systems.

Availability

SN74F657DWR is available at Aetrix Electronics and suitable for memory bus interfaces, industrial PLC modules, backplane data links, and legacy computer expansion bus designs requiring stable component supply and long-term obsolescence management.

Supply support for SN74F657DWR 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 with broad industrial, automotive, and communications reach.

The SN74F657DWR belongs to TI's 74F Fast TTL logic family, engineered for high-speed, low-latency bus interfacing in commercial-grade computing and control systems where reliability and timing precision are critical.

FAQ

What is the function of the ODD/EVEN pin on the SN74F657DWR?

The ODD/EVEN pin configures the internal parity generator/checker to produce or validate odd (high) or even (low) parity. During A→B transmission, it determines the logic state of the PARITY output; during B→A reception, it defines the expected parity for ERR assertion. This pin must be held static during each transaction and is not dynamically switchable mid-cycle.

Can SN74F657DWR operate with a 3.3 V supply?

No. The SN74F657DWR is specified only for 4.5 V to 5.5 V operation per its recommended conditions. Applying 3.3 V violates the minimum VCC requirement and will result in undefined logic states, failed parity checks, and unreliable 3-state control - it is not 3.3 V tolerant and lacks level-shifting capability.

How does the ERR output behave during SN74F657DWR receive mode?

In receive mode (T/R low), ERR goes high only when the number of high bits on B1–B8 matches the expected parity defined by ODD/EVEN and the PARITY input. For example, with ODD/EVEN low (even parity) and four high bits on B port, ERR is high if PARITY input is low - confirming correct parity. Mismatch forces ERR low, signaling an error.

Is SN74F657DWR pin-compatible with SN74F245DW?

SN74F657DWR and SN74F245DW share identical SOIC-24 pinouts for A1–A8, B1–B8, T/R, OE, VCC, and GND, but SN74F657DWR repurposes pins 11 (ERR), 12 (PARITY), and 13 (ODD/EVEN) for parity functions - these pins are no-connect or NC on SN74F245DW. Direct substitution requires PCB modification unless those pins are unused.

What is the maximum data rate supported by SN74F657DWR in a typical bus configuration?

Based on tPLH/tPHL ≤ 8 ns (max) and setup/hold margin requirements, SN74F657DWR supports reliable operation up to approximately 80 MHz in point-to-point configurations with 50 pF load. In multi-drop or longer trace scenarios, derating to 50 MHz is recommended to maintain timing closure and signal integrity.