Renesas X24C44SI

Overview

X24C44SI from Xicor is a serial 256-bit nonvolatile static RAM (NOVRAM) with 16 × 16 organization, integrating SRAM and EEPROM bit-by-bit on a single die. It operates from a single 5V supply, supports auto RECALL on power-up, completes STORE in ≤5 ms and RECALL in ≤2 µs, and targets microcontroller-based systems requiring persistent data retention without battery backup - e.g., configuration storage in industrial controllers.

For engineers reviewing the X24C44SI datasheet, X24C44SI pinout, X24C44SI application, or X24C44SI equivalent, this page delivers verified timing parameters, hardware/software control logic for STORE/RECALL, TTL/CMOS compatibility, low-power standby current (50 µA), and package-specific pin mapping for SOIC-8.

Technical Context

The X24C44SI implements a dual-array architecture where 256-bit SRAM is overlaid bit-for-bit with EEPROM using Advanced CMOS Floating Gate technology. Its instruction register accepts 8-bit opcodes via DI/SK, with MSB-first serial protocol compatible with 8051 and COPS™ interfaces.

Nonvolatile operations require coordinated latching: STORE requires both the "write enable" latch (set by WREN) and "previous recall" latch (set by RCL or RECALL pin assertion); RECALL can be triggered either by software RCL instruction or hardware RECALL pin low. Power-up RECALL transfers EEPROM to RAM but does not set the "previous recall" latch.

Key Specifications

Pinout & Package

Package: 8-lead SOIC (S8), surface-mount, 150 mil body width, 1.27 mm pitch.

Key Features

Applications

Equivalent & Alternatives

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

Compared with X24C44SI, the X24C44PI offers identical functionality but higher standby current and through-hole mounting, while the X24C44DI extends temperature range to –55°C/+125°C at the cost of ceramic packaging and higher unit price - neither is pin-compatible with SOIC-8 layout, requiring PCB redesign.

Availability

X24C44SI is available at Aetrix Electronics and suitable for industrial sensor calibration storage, PLC configuration backup, medical device setup parameters, and automotive ECU trim settings requiring stable component supply across extended product lifecycles.

Supply support for X24C44SI 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. Known for innovations in EEPROM-integrated SRAM and digital potentiometers.

The X24C44SI belongs to Xicor's NOVRAM product line, designed specifically for embedded systems needing battery-free, fast-access nonvolatile memory with guaranteed 100-year data retention and 1M STORE endurance.

FAQ

What is the primary function of the X24C44SI in an embedded system?

The X24C44SI serves as a serial nonvolatile static RAM (NOVRAM), combining 256-bit SRAM and EEPROM in a bit-mapped overlay. It enables immediate read/write access to volatile RAM while preserving critical data in EEPROM across power cycles. Its core function is to eliminate battery backup in microcontroller systems requiring persistent configuration or calibration data - for example, storing sensor offsets that must survive power loss without degradation over decades.

How does the X24C44SI handle power-up initialization?

The X24C44SI performs an automatic RECALL operation on power-up, transferring stored EEPROM data into the SRAM array within ≤2 µs. However, this hardware-initiated RECALL does not set the "previous recall" latch - a separate software RCL instruction or hardware RECALL pin assertion is required before any STORE operation can be executed. This design prevents accidental EEPROM writes during boot and enforces intentional data persistence.

What are the exact conditions required to execute a STORE operation on the X24C44SI?

A STORE operation on the X24C44SI requires three simultaneous conditions: (1) the "write enable" latch must be set via WREN instruction, (2) the "previous recall" latch must be set via RCL instruction or RECALL pin LOW, and (3) either the STO instruction must be issued or the STORE pin driven LOW. If any condition is unmet, the STORE is inhibited - this dual-latch mechanism prevents inadvertent EEPROM corruption during power transients or software faults.

Can the X24C44SI be interfaced directly with an 8051 microcontroller?

Yes, the X24C44SI is explicitly designed for direct interface with 8051-family microcontrollers. Its serial protocol uses CE, SK, DI, and DO signals compatible with standard 8051 I/O ports; it requires no external level shifters due to TTL/CMOS input compatibility and 5V-only operation. The datasheet confirms COPS™ and 8051 compatibility, and timing parameters (e.g., t_DS = 400 ns, t_SKH = 400 ns) align with 8051 port toggle speeds at typical clock frequencies.

What is the significance of the 50 µA standby current specification for the X24C44SI?

With 50 µA maximum standby current (measured at CMOS input levels and V_SS CE), the X24C44SI enables true low-power system design - for instance, in battery-operated remote sensors where the host MCU sleeps for minutes between readings. This value is 20× lower than the 1 mA standby of the PDIP variant (X24C44PI), making the SOIC version essential for energy-constrained applications where cumulative leakage must remain below 100 µA across all peripherals.