Texas Instruments CD74HCT40105E

Overview

CD74HCT40105E from Texas Instruments is a high-speed CMOS 4-bit × 16-word first-in-first-out (FIFO) register with independent asynchronous input/output control, three-state outputs, master reset, and data-ready status flags (DIR/DOR). It operates from 4.5V to 5.5V, supports -55°C to +125°C, and enables bit-rate smoothing between mismatched clock domains in CPU-terminal buffering and radar data acquisition systems.

For engineers reviewing the CD74HCT40105E datasheet, CD74HCT40105E pinout, CD74HCT40105E application, or CD74HCT40105E equivalent, key selection criteria include its 4.5–5.5V HCT logic compatibility with LSTTL inputs, 16-word elastic storage depth, DIR/DOR flag timing behavior, and PDIP-16 package for through-hole prototyping and industrial control interfaces.

Technical Context

The CD74HCT40105E implements a marker-bit-controlled FIFO architecture where 16 control flip-flops track data occupancy per 4-bit word position. Data propagation occurs via ripple-through of "1" markers, enabling automatic shifting without external clock synchronization between SI and SO paths.

Its three-state outputs (Q0–Q3) are decoupled from shift-out control, eliminating the CD40105B's restriction on OE transitions during SO pulses. The DIR and DOR flags provide real-time full/empty status, and master reset clears only control logic-not stored data-preserving integrity during partial reloads.

Key Specifications

Pinout & Package

CD74HCT40105E uses a 16-pin plastic dual in-line package (PDIP), with 0.3-inch body width and standard through-hole mounting. Pin 1 is located at the top-left corner when viewed from the top with notch or dot orientation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar FIFO register applications.

Compared with CD74HC40105E, the CD74HCT40105E provides guaranteed LSTTL input compatibility essential for legacy integration, while SN74ACT2227N offers higher data width and speed at the cost of added control complexity and no native status signaling.

Availability

CD74HCT40105E is available at Aetrix Electronics and suitable for CPU-terminal buffering, radar data acquisition, and peripheral interfacing requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for CD74HCT40105E 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 delivering analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The CD74HCT40105E belongs to TI's High-Speed CMOS Logic family, designed specifically for asynchronous data buffering in mixed-technology systems where LSTTL compatibility, wide temperature operation, and self-synchronizing FIFO behavior are required.

FAQ

What is the primary function of the CD74HCT40105E?

The CD74HCT40105E is a 4-bit × 16-word first-in-first-out (FIFO) register that buffers asynchronous data streams using marker-bit ripple-through logic. It features independent shift-in/shift-out controls, DIR/DOR status flags, three-state outputs, and master reset - enabling reliable handshaking between mismatched clock domains without external timing circuitry. Its HCT logic ensures direct compatibility with LSTTL inputs.

How does the CD74HCT40105E handle full and empty conditions?

The CD74HCT40105E uses open-drain DIR (Data-In Ready) and DOR (Data-Out Ready) flags to signal FIFO status. DIR goes HIGH when at least one location is vacant; it goes LOW when all 16 words are filled. DOR goes HIGH when valid data occupies the output position; it remains LOW when the FIFO is empty. Both flags update automatically via internal marker-bit propagation - no software polling or external logic is required to monitor occupancy.

Can the CD74HCT40105E be cascaded to increase depth or width?

Yes, the CD74HCT40105E supports cascading: connecting DIR to SO and DOR to SI extends FIFO depth beyond 16 words. For wider data paths (e.g., 8-bit), multiple CD74HCT40105E devices can be paralleled with AND-gated DIR/DOR signals driving shared SI/SO lines. A master reset pulse must be applied after power-up in cascaded configurations to initialize all control logic consistently.

What is the role of the Master Reset (MR) pin on the CD74HCT40105E?

The MR pin on the CD74HCT40105E is an active-HIGH signal that resets all 16 control flip-flops to "0", clearing DIR and DOR flags and declaring all positions vacant. Critically, MR does not erase data stored in the 4-bit latches - only the occupancy markers are reset. This allows partial reloads without losing previously loaded words, and if SI is HIGH during reset, incoming D0–D3 data is immediately accepted into position 1 upon MR deactivation.

Is the CD74HCT40105E pin-compatible with the CD40105B?

No, the CD74HCT40105E is not pin-compatible with the CD40105B. While functionally similar as a 4-bit × 16-word FIFO, the CD74HCT40105E reassigns pin functions: CD40105B uses pins 1/2 for VCC/GND and pins 15/16 for DOR/Q3, whereas CD74HCT40105E places VCC at pin 16 and GND at pin 8, with DOR at pin 9 and Q3 at pin 13. Direct replacement requires PCB layout revision.