Texas Instruments SN74F657DWRG4

Overview

SN74F657DWRG4 from Texas Instruments is an octal transceiver with integrated 8-bit parity generator/checker and 3-state outputs, designed for bidirectional data 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 for robust bus driving. Used in legacy industrial backplanes and memory-mapped I/O subsystems requiring error detection.

For engineers reviewing the SN74F657DWRG4 datasheet, SN74F657DWRG4 pinout, SN74F657DWRG4 application, or SN74F657DWRG4 equivalent, key selection criteria include its dual-function integration (transceiver + parity logic), asymmetric drive strength (24 mA A-port / 64 mA B-port), 3-state enable timing (tPZH/tPLZ ≤ 9 ns), and operation over 0°C to 70°C commercial temperature range.

Technical Context

The SN74F657DWRG4 implements a synchronous, combinational parity generator/checker alongside eight noninverting bidirectional buffers - not a microcontroller peripheral or serial protocol engine. Its parity logic operates on all eight A- or B-port bits simultaneously, with PARITY output during transmit (T/R = H) and PARITY input during receive (T/R = L), while ERR asserts high only when parity matches expected odd/even state.

Direction control is strictly level-sensitive: T/R high enables A→B transmission and disables B→A path; T/R low enables B→A reception and disables A→B path. OE independently places both A and B ports into high-impedance state regardless of T/R, with tPZH/tPLZ specifying 3-state transition delays relative to OE edge.

Key Specifications

Pinout & Package

SN74F657DWRG4 is housed in a 24-pin SOIC (DW) package with 300-mil width, RoHS-compliant NiPdAu lead finish, and moisture sensitivity level 1 (unlimited floor life at ≤30°C/60% RH).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74F657DWRG4, SN74F245DW lacks parity functionality entirely and requires additional components, while SN74LS657N trades off speed, drive strength, and input loading for lower cost and broader legacy availability - neither offers pin-compatible parity integration.

Availability

SN74F657DWRG4 is available at Aetrix Electronics and suitable for industrial backplane bus design, legacy memory-mapped I/O interfacing, and test equipment data acquisition requiring stable component supply and long-term obsolescence management.

Supply support for SN74F657DWRG4 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 ICs with broad industrial and automotive qualification.

The SN74F657DWRG4 belongs to TI's 74F fast TTL logic family, engineered for high-speed, low-noise bus interfacing in commercial-temperature embedded systems where reliability and deterministic timing are essential.

FAQ

What is the function of the ODD/EVEN pin on the SN74F657DWRG4?

The ODD/EVEN pin on the SN74F657DWRG4 configures the parity mode: logic low selects even parity, logic high selects odd parity. During transmit (T/R = H), it determines the parity bit value generated at the PARITY output; during receive (T/R = L), it defines the expected parity state used to validate incoming data at the B port and assert ERR accordingly. This pin must be held static during each transaction.

Can the SN74F657DWRG4 operate with a 3.3 V supply?

No, the SN74F657DWRG4 is specified only for 4.5 V to 5.5 V operation and is not 3.3 V compatible. Its input thresholds (VIH = 2 V min, VIL = 0.8 V max) and output drive characteristics are optimized for 5 V TTL logic families. Applying 3.3 V to VCC may result in undefined behavior, insufficient noise margin, or failure to meet timing specifications.

How does the ERR output behave during receive mode on the SN74F657DWRG4?

During receive mode (T/R = L), the ERR output on the SN74F657DWRG4 goes high when the number of high bits on the B port plus the PARITY input matches the selected odd/even mode - indicating no parity error. For example, with ODD/EVEN = L (even parity) and an even number of highs on B port, ERR = H if PARITY = L; ERR = L indicates a detected error. ERR is active only after full propagation through B→A and A→PARITY paths.

Is the SN74F657DWRG4 pin-compatible with the SN74F245?

No, the SN74F657DWRG4 is not pin-compatible with the SN74F245. While both are 24-pin SOIC transceivers, SN74F657DWRG4 replaces two functions (transceiver + parity) and uses pins 11 (ERR), 13 (PARITY), and 3 (ODD/EVEN) for parity control - absent on SN74F245. Direct substitution would require PCB redesign and firmware adaptation for ERR/ODD/EVEN handling.

What is the maximum capacitive load the SN74F657DWRG4 can drive on its B-port outputs?

The SN74F657DWRG4 B-port outputs are characterized for CL = 50 pF in switching specifications, but its 64 mA sink capability supports heavier loads. With proper termination and layout, it reliably drives up to 100 pF while maintaining tPHL ≤ 8 ns at VCC = 5 V. Exceeding this requires verifying VOL ≤ 0.55 V under actual load conditions, as higher capacitance increases transition time and ground bounce risk.