onsemi MC74F657BDWR

Overview

MC74F657BDWR from ON Semiconductor (formerly Motorola) is a FAST Schottky TTL octal bidirectional transceiver with integrated 8-bit parity generator/checker and 3-state outputs. It features A-port sinking capability of 24 mA, B-port sinking of 64 mA, 15 mA sourcing on B outputs, and operates across 0°C to +70°C at VCC = 4.5–5.5 V. It is used in bus-oriented systems requiring error-checked data transfer between subsystems.

For engineers reviewing the MC74F657BDWR datasheet, pinout, applications, or equivalent options, key selection factors include its dual-directional bus control via T/R input, real-time parity validation on 8-bit data paths, guaranteed 3-state isolation during power-up/down, and SOIC-24 packaging for high-density PCB layouts.

Technical Context

The MC74F657BDWR implements a synchronous bidirectional data path controlled by the Transmit/Receive (T/R) input: active-HIGH enables A→B transmission; active-LOW enables B→A reception. Its parity logic computes even/odd parity over A0–A7 or B0–B7 inputs and compares against the EVEN/ODD control input to assert ERROR when mismatched.

It integrates two functional blocks - an octal non-inverting buffer array with independent 3-state enable (OE) and direction (T/R) control, and a dedicated 8-bit parity generator/checker with separate PARITY and ERROR outputs. All outputs exhibit glitchless behavior during power transitions and maintain high-impedance states when powered off.

Key Specifications

Pinout & Package

MC74F657BDWR is housed in a 24-pin SOIC (Small Outline Integrated Circuit) package per case outline 751E-03, with 300 mil body width and gull-wing leads. The package supports surface-mount reflow assembly and provides mechanical stability for high-vibration applications.

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 MC74F657ADWR, the MC74F657BDWR delivers optimal balance of speed, package reliability, and thermal performance for volume-manufactured industrial bus interfaces - especially where SOIC-24 footprint and sub-7 ns latency are mandatory.

Availability

MC74F657BDWR is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy computer expansion systems, automated test equipment data acquisition, and avionics diagnostic ports requiring stable component supply and long-term obsolescence management.

Supply support for MC74F657BDWR 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 is a global semiconductor supplier delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and IoT applications.

The MC74F657BDWR belongs to ON Semiconductor's legacy FAST TTL logic family, designed specifically for high-speed, parity-protected parallel bus architectures in mission-critical industrial and aerospace systems.

FAQ

What is the maximum clock frequency supported by MC74F657BDWR?

The MC74F657BDWR does not operate on a clock signal - it is an asynchronous TTL transceiver. Its usable data rate depends on propagation delay and system timing margins. With a maximum An→Bn delay of 6.5 ns and setup/hold times inherent to TTL logic families, it reliably supports bus cycles up to approximately 100 MHz in well-designed layouts. System-level timing validation is required for each implementation of MC74F657BDWR.

Does MC74F657BDWR support hot-swapping on a live bus?

Yes - MC74F657BDWR exhibits glitchless outputs during power-up and power-down, and maintains high-impedance outputs when unpowered. When OE is held HIGH during insertion, all I/Os remain in 3-state, preventing bus contention. This behavior makes MC74F657BDWR suitable for controlled hot-swap applications, provided power sequencing follows manufacturer-recommended ramp rates.

How is parity calculated and checked in MC74F657BDWR?

The MC74F657BDWR computes parity over the eight active data inputs (A0–A7 during transmit, B0–B7 during receive) using internal XOR logic. The EVEN/ODD input selects expected parity type. If the computed result matches the selected mode, ERROR remains LOW; a mismatch forces ERROR HIGH. PARITY output reflects the computed bit value, enabling use as generator or checker depending on system configuration - all within MC74F657BDWR's fixed logic block.

Can MC74F657BDWR interface directly with CMOS logic?

MC74F657BDWR outputs meet TTL voltage thresholds (VOH ≥ 2.4 V, VOL ≤ 0.5 V), which are compatible with 5 V CMOS inputs (VIH ≥ 3.5 V, VIL ≤ 1.5 V) only with margin. Direct connection may cause marginal noise immunity or increased static power in CMOS receivers. For reliable interfacing, level-shifting buffers or pull-up resistors are recommended. MC74F657BDWR is optimized for TTL-to-TTL interconnect, not mixed-logic domain bridging.

What is the meaning of the 'B' suffix in MC74F657BDWR?

The 'B' in MC74F657BDWR denotes the faster speed grade within the F657 family: MC74F657B offers tighter AC specifications than MC74F657A - notably reduced propagation delays (e.g., 6.5 ns max An→Bn vs. 7.5 ns) and faster enable/disable times. The 'DWR' suffix specifies SOIC-24 package (DW) with tape-and-reel packaging (R). Thus, MC74F657BDWR is the high-speed, surface-mount variant optimized for automated manufacturing.