Texas Instruments SN74F657DW

Overview

SN74F657DW 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 64 mA sink capability at B-port outputs, and operates across 4.5–5.5 V supply at 0°C to 70°C. Used in legacy industrial backplanes and memory-mapped I/O subsystems requiring hardware parity validation.

For engineers reviewing the SN74F657DW datasheet, SN74F657DW pinout, SN74F657DW application, or SN74F657DW equivalent, key selection criteria include its dual-mode parity logic (ODD/EVEN-selectable), ERR output behavior during receive mode, 3-state enable timing (tPZH/tPLZ < 9 ns), and SOIC-24 package compatibility with 5-V TTL bus architectures.

Technical Context

The SN74F657DW integrates two functional blocks: an octal noninverting transceiver (A↔B) and a dedicated 8-bit parity generator/checker. Data direction is controlled by the T/R input, while OE enables/disables all outputs into high-impedance state. PARITY serves as output during transmit (T/R = H) and input during receive (T/R = L).

Parity evaluation is synchronized to B-port inputs when receiving: ERR asserts high only when the count of high bits on B1–B8 matches the ODD/EVEN setting and the PARITY input reflects correct parity. Switching delays are specified under 50 pF load with 500 Ω source termination, supporting sub-10 ns propagation for critical bus timing paths.

Key Specifications

Pinout & Package

SN74F657DW uses a 24-pin SOIC (DW) package with 300-mil width, compliant with JEDEC MS-013, and rated MSL-1 for unlimited reflow exposure. Pin spacing is 1.27 mm, body width 7.5 mm, and total length 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 SN74F657DW, SN74F245DW omits parity logic entirely-reducing component count but eliminating hardware-level error detection-while SN74F280BN forces a two-chip solution with higher board cost and routing complexity, making SN74F657DW the optimal single-package choice for parity-critical bus interfaces.

Availability

SN74F657DW is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy memory-mapped I/O subsystems, and telecom line card buses requiring stable component supply and long-term obsolescence management.

Supply support for SN74F657DW 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 for industrial, automotive, and communications markets.

The SN74F657DW belongs to TI's 74F Fast TTL logic family, engineered for high-speed, low-power bus interfacing in mission-critical systems where reliability and timing predictability are essential.

FAQ

What is the maximum sink current supported by the B-port outputs of the SN74F657DW?

The SN74F657DW B-port outputs (B1–B8) support up to 64 mA sink current per pin under recommended operating conditions (VCC = 4.5 V, IOL = 64 mA). This rating enables direct drive of multiple TTL inputs or moderate-capacitance bus segments without external buffering, and is verified in the electrical characteristics table of the SN74F657DW datasheet.

How does the ERR output behave during receive mode on the SN74F657DW?

During receive mode (T/R = L), the SN74F657DW evaluates the number of high bits on B1–B8 and compares it against the ODD/EVEN setting and the PARITY input. ERR goes high only when the parity condition matches-e.g., for even parity (ODD/EVEN = L), ERR = H if B-port high-bit count is even and PARITY = L. This behavior is defined in the function table and confirmed in the logic diagram of the SN74F657DW.

Can the SN74F657DW operate with a 3.3-V supply?

No, the SN74F657DW is a 74F-family TTL device specified for 4.5–5.5 V operation only. Its input thresholds (VIH = 2 V min, VIL = 0.8 V max), output drive strength, and internal logic levels are optimized for 5-V systems. Using 3.3 V violates recommended operating conditions and risks unreliable switching or excessive ICCZ current, as documented in the SN74F657DW absolute maximum and recommended operating conditions tables.

What is the purpose of the ODD/EVEN pin on the SN74F657DW?

The ODD/EVEN pin on the SN74F657DW selects the parity scheme used by the integrated generator/checker: logic low configures even parity, logic high configures odd parity. During transmit (T/R = H), it determines the PARITY output state; during receive (T/R = L), it defines the expected parity condition for ERR assertion. This pin enables runtime parity protocol alignment without hardware modification in the SN74F657DW.

Is the SN74F657DW pin-compatible with other 24-pin SOIC transceivers like the SN74F245DW?

The SN74F657DW shares the same SOIC-24 (DW) package and pin count as SN74F245DW, but pin functions differ significantly: SN74F657DW dedicates pins to PARITY, ERR, and ODD/EVEN not present on SN74F245DW. Therefore, it is not pin-compatible-direct replacement would require PCB redesign. This distinction is clearly shown in the logic symbol and pinout diagrams of the SN74F657DW datasheet.