Renesas X24C44P

Overview

X24C44P from Xicor is a serial nonvolatile static RAM (NOVRAM) integrating 256-bit SRAM (16 × 16) bit-mapped with EEPROM for persistent storage, operating from a single 5V ±10% supply, featuring hardware STORE/RECALL pins and software-controlled WREN/STO/RCL instructions, and used in microcontroller-based systems requiring automatic power-up data restoration.

For engineers reviewing the X24C44P datasheet, X24C44P pinout, X24C44P application, or X24C44P equivalent, key selection considerations include its 5ms STORE time, 2µs RECALL latency, 1,000,000 STORE endurance, 100-year data retention, and compatibility with 8051/COPS™ serial interfaces in space-constrained embedded designs.

Technical Context

The X24C44P implements a dual-array architecture where SRAM and EEPROM are overlaid bit-for-bit, enabling atomic STORE (RAM→EEPROM) and RECALL (EEPROM→RAM) operations via dedicated hardware pins or instruction codes. Its instruction register accepts 8-bit opcodes with MSB=1, address bits A3–A0 in READ/WRITE, and operation codes in bits 2–0.

Operation requires two latches: a write-enable latch (set by WREN, reset by WRDS or power-up) and a "previous recall" latch (set only by RCL or RECALL pin assertion, not by power-up recall). Both latches must be asserted before a STORE executes, preventing inadvertent EEPROM writes during power transitions.

Key Specifications

Pinout & Package

Package: 8-lead plastic DIP (P8), 0.300-inch width, through-hole mount, RoHS-unspecified legacy construction.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar serial nonvolatile RAM applications.

Compared with X24C44P, X24C02P provides higher density but no volatile working layer or hardware acceleration, while FM24C04 removes endurance limits yet sacrifices the precise STORE/RECALL control and power-up behavior essential for deterministic embedded state recovery.

Availability

X24C44P is available at Aetrix Electronics and suitable for industrial sensor calibration, medical device configuration, automotive body control modules, point-of-sale terminal settings, and legacy microcontroller system upgrades requiring stable component supply and long-term obsolescence management.

Supply support for X24C44P 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

Xicor, Inc. was a fabless semiconductor company specializing in nonvolatile memory and programmable analog ICs, acquired by Intersil in 2001 and later integrated into Renesas Electronics.

The X24C44P belongs to Xicor's NOVRAM product line, designed specifically for embedded systems needing seamless integration of fast SRAM access with EEPROM persistence, targeting 8051- and COPS™-based platforms with minimal I/O and power constraints.

FAQ

What is the function of the RECALL pin on the X24C44P?

The RECALL pin on the X24C44P is an active-LOW hardware input that triggers an immediate transfer of data from the EEPROM array into the SRAM array in ≤2µs. Unlike the power-up RECALL, asserting this pin also sets the internal "previous recall" latch, which is required-alongside the write-enable latch-for subsequent STORE operations. This enables deterministic, CPU-independent state restoration critical in safety- or timing-sensitive applications.

How does the X24C44P prevent accidental STORE operations during power transitions?

The X24C44P prevents accidental STORE operations using two independent latches: the write-enable latch (set by WREN, reset by WRDS or power-up) and the "previous recall" latch (set only by RCL instruction or RECALL pin, not by power-up). Both must be asserted before any STORE executes. During power-down, holding RECALL LOW, CE LOW, or STORE HIGH maintains latch states safely, blocking unintended EEPROM writes even under unstable V_CC.

Can the X24C44P operate with modern 3.3V microcontrollers?

No, the X24C44P is specified exclusively for 5V ±10% operation and features TTL/CMOS-compatible inputs-not 3.3V-tolerant ones. Its V_IL (0.8V max) and V_IH (2.0V min) thresholds align with 5V logic families. Interfacing with 3.3V microcontrollers requires level-shifting circuitry on CE, SK, DI, DO, STORE, and RECALL lines to avoid undefined behavior or damage.

What is the significance of the "truncated D0" behavior during READ operations on the X24C44P?

During a READ operation, the X24C44P outputs D0 (the first data bit) on the falling edge of the 8th SK clock cycle, while subsequent bits (D1–D15) are clocked on rising edges. This truncation allows the host to switch a shared I/O line from output to input between instruction completion and data output, supporting bidirectional bus implementations like those used with 8051 ports. It also ensures valid D1 appears on the 9th SK rising edge.

Is the X24C44P still in production, and what support does Aetrix Electronics provide for it?

The X24C44P is marked "Obsolete Product" in its official datasheet (Rev 1.0, 6/22/00), and Xicor discontinued it following its acquisition by Intersil. Aetrix Electronics maintains a verified legacy inventory with full traceability, offers extended lifecycle coordination, and supports design-in continuity through cross-reference guidance, application notes (AN3, AN7, AN15, etc.), and technical documentation for legacy system maintenance and replacement planning.