onsemi MC74F657BDW

Overview

MC74F657BDW from ON Semiconductor (formerly Motorola) is an octal bidirectional transceiver with integrated 8-bit parity generator/checker and 3-state outputs in SOIC-24 package. It supports bus-oriented data transfer between A and B ports, provides 64 mA sink capability at B outputs, and features glitchless power-up/down behavior for reliable system initialization. Used in legacy industrial backplane and memory expansion interfaces.

For engineers reviewing the MC74F657BDW datasheet, pinout, applications, or equivalent options, key selection considerations include its 2.0–6.5 ns propagation delay (A→B/B→A), 64 mA B-port drive strength, EVEN/ODD-selectable parity mode, ERROR flag generation, and guaranteed 0°C to +70°C operation with 4.5–5.5 V supply.

Technical Context

The MC74F657BDW implements dual-function logic: eight non-inverting bidirectional buffers controlled by T/R and OE inputs, plus a dedicated 8-bit parity generator/checker with selectable even/odd mode and ERROR output assertion on parity mismatch. Its Fast Schottky TTL architecture ensures compatibility with 74F-series timing and voltage thresholds.

All outputs enter high-impedance state when OE is HIGH; direction is determined solely by T/R (HIGH = A→B transmit, LOW = B→A receive). The parity block evaluates all eight A-port inputs or B-port inputs depending on T/R state and asserts ERROR when detected parity does not match the EVEN/ODD setting - enabling real-time bus integrity monitoring without external logic.

Key Specifications

Pinout & Package

MC74F657BDW is housed in a 24-pin SOIC package (case 751E-03), 7.5 mm wide, with 1.27 mm pitch. Pin 1 is top-left corner marked dot; pin 24 is bottom-right.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74F657N and 74F657PC, the MC74F657BDW offers superior thermal dissipation in SOIC packaging, tighter 6.5 ns max propagation delay, and guaranteed 0°C–70°C operation - making it the preferred choice for production-grade industrial backplane designs requiring long-term reliability and timing precision.

Availability

MC74F657BDW is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy memory expansion systems, and telecom line card control requiring stable component supply despite end-of-life status.

Supply support for MC74F657BDW 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

ON Semiconductor (formerly Motorola Semiconductor) is a global supplier of high-performance silicon solutions for automotive, industrial, cloud computing, and IoT applications.

The MC74F657BDW belongs to the 74F Fast TTL logic family, designed specifically for high-speed, low-power bus-oriented systems requiring deterministic timing, robust drive strength, and hardware-level data integrity checking.

FAQ

What is the operating temperature range for MC74F657BDW?

The MC74F657BDW is specified for operation from 0°C to +70°C ambient temperature. This range is guaranteed per its DC and AC electrical characteristics tables, and applies to all functional modes including transmit, receive, and high-impedance states. The device must be operated within this range to ensure compliance with its published propagation delays, drive currents, and voltage thresholds. MC74F657BDW performance outside this range is not characterized or warranted.

How does the PARITY output behave during transmit versus receive mode?

In transmit mode (T/R = HIGH), the PARITY output reflects the even/odd parity of the A-port inputs (A0–A7); in receive mode (T/R = LOW), it reflects the parity of the B-port inputs (B0–B7). The PARITY bit is always generated based on the source port of the active data path. MC74F657BDW does not generate parity on both ports simultaneously - the active port is strictly determined by T/R state, and PARITY updates synchronously with data transitions on that port.

Can MC74F657BDW be used with 3.3 V logic systems?

No, MC74F657BDW is a 5 V Fast TTL device requiring VCC between 4.5 V and 5.5 V. Its input thresholds (VIH = 2.0 V, VIL = 0.8 V) and output levels (VOH = 2.4 V min at –3 mA) are incompatible with 3.3 V CMOS logic families without level translation. Direct connection to 3.3 V systems risks incorrect logic interpretation or excessive current draw. MC74F657BDW must be used in 5 V-only domains or interfaced via dedicated level shifters.

What happens to the ERROR output when OE is HIGH?

When OE is HIGH, all outputs including ERROR enter high-impedance state - the ERROR pin becomes electrically disconnected and cannot assert a valid logic level. ERROR only drives active HIGH or LOW when OE is LOW and the device is enabled. During OE HIGH, parity evaluation continues internally, but the result is not presented on the ERROR pin. MC74F657BDW does not provide tri-state-aware parity latching - ERROR is purely an output-driven signal.

Is MC74F657BDW pin-compatible with MC74F657ADW?

Yes, MC74F657BDW is pin-compatible with MC74F657ADW - both use identical SOIC-24 (751E-03) packaging and share identical pin assignments, logic functions, and DC/AC specifications except for propagation delay. The 'B' version offers faster timing (6.5 ns max A↔B delay vs. 7.5 ns for 'A'), but requires no PCB changes. MC74F657BDW can directly replace MC74F657ADW in existing layouts where improved speed is beneficial.