NXP Semiconductors N74F657D,623

Overview

N74F657D,623 from Philips Semiconductors is an octal transceiver with integrated 8-bit parity generator/checker in a 24-pin plastic small outline (SO24) package. It provides bidirectional data flow between A and B ports, 3-state outputs, and real-time parity generation or checking based on ODD/EVEN selection - delivering 64 mA sink capability at B ports and 24 mA at A ports for robust bus interfacing in industrial control backplanes.

For engineers reviewing the N74F657D,623 datasheet, N74F657D,623 pinout, N74F657D,623 application, or N74F657D,623 equivalent, key selection considerations include its dual-role parity logic (generator during transmit, checker during receive), ERROR output assertion timing relative to B-to-A propagation plus A-to-PARITY delay, and compatibility with FAST TTL-level signaling across –40 °C to +85 °C.

Technical Context

The N74F657D,623 integrates transceiver and parity logic into a single die: non-inverting 3-state buffers route data bidirectionally under T/R control, while the parity engine evaluates bit count on A port (transmit mode) or B port (receive mode) and asserts ERROR when parity mismatch occurs. The PARITY pin serves as output in transmit mode and input in receive mode.

Its electrical behavior is defined by FAST TTL-compatible thresholds (V_IL = 0.8 V, V_IH = 2.0 V), guaranteed I_OL of 64 mA on B0–B7/ERROR/PARITY, and low input loading (I_IL/I_IH ≤ 40 µA on T/R/OE). Propagation delays are specified up to 25 ns max over full industrial temperature range with 50 pF load.

Key Specifications

Pinout & Package

Package: SO24 - plastic small outline, 24-lead, 7.5 mm body width (SOT137-1), surface-mount compatible.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74F657N and 74ACT657, the N74F657D,623 uniquely combines industrial temperature support, SOIC packaging for high-density layouts, and full 64 mA B-port drive - making it the sole option for ruggedized, space-constrained, high-current bus applications.

Availability

N74F657D,623 is available at Aetrix Electronics and suitable for industrial backplane buses, legacy parallel interfaces, telecom line cards, and test equipment data paths requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for N74F657D,623 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

Philips Semiconductors (now NXP Semiconductors) is a global semiconductor innovator with leadership in logic, analog, and interface solutions for industrial and communications markets.

The 74F657 family was designed specifically for high-reliability, parity-protected parallel data transfer in industrial control and telecom infrastructure - emphasizing robust drive strength, low input loading, and deterministic error reporting.

FAQ

What is the function of the PARITY pin on the N74F657D,623?

The PARITY pin on the N74F657D,623 serves a dual role: during transmit mode (T/R = HIGH), it outputs the computed parity bit based on A-port data and ODD/EVEN setting; during receive mode (T/R = LOW), it accepts the incoming parity bit from the B bus for error checking. This dynamic I/O behavior is intrinsic to the N74F657D,623's integrated parity generator/checker architecture and requires correct mode sequencing in system firmware.

Does the N74F657D,623 support both odd and even parity configurations?

Yes, the N74F657D,623 supports both odd and even parity via the ODD/EVEN input pin: a LOW level selects even parity, and a HIGH level selects odd parity. This selection determines both the PARITY output level during transmit and the expected parity state during receive - enabling seamless integration into either parity scheme without external logic. The N74F657D,623 implements this fully in hardware with no latency penalty.

What is the maximum allowable propagation delay for ERROR assertion in receive mode on the N74F657D,623?

In receive mode (T/R = LOW), valid ERROR assertion on the N74F657D,623 requires cumulative delay of B→A propagation plus A→PARITY propagation - specified up to 25.0 ns max at –40 °C to +85 °C with 50 pF load. Therefore, system timing must allocate ≥25 ns from B-port data stabilization to ERROR pin validity. This constraint is inherent to the N74F657D,623's internal signal path and cannot be reduced by external means.

Can the N74F657D,623 operate with a 3.3 V supply?

No, the N74F657D,623 is a FAST TTL device requiring V_CC = 4.5 V to 5.5 V and is not 3.3 V compatible. Its input thresholds (V_IH = 2.0 V min, V_IL = 0.8 V max) and output drive characteristics are optimized for 5 V operation. Using 3.3 V will result in undefined logic states and insufficient output swing. For 3.3 V systems, consider alternatives like 74ACT657 - but note the N74F657D,623 itself mandates 5 V.

How does the N74F657D,623 handle bus contention when both A and B ports are enabled simultaneously?

The N74F657D,623 prevents bus contention through strict directional control: only one direction (A→B or B→A) is active per T/R state, and OE must be LOW for any output to be enabled. Simultaneous A→B and B→A activation is electrically impossible - the N74F657D,623's internal logic gates ensure mutual exclusion. If OE is HIGH, all outputs enter high-impedance regardless of T/R, eliminating contention risk during bus arbitration.