Renesas 71321LA55J8

Overview

71321LA55J8 from IDT (now Renesas) is a high-speed 2K × 8 dual-port static RAM with interrupt and BUSY arbitration logic, designed as a MASTER device for interprocessor communication in real-time embedded systems. It delivers 55 ns max read/write cycle time, 2V data retention in battery backup mode, industrial temperature operation (–40°C to +85°C), and supports fully asynchronous dual-port access with independent control/address/I/O on left and right ports.

For engineers reviewing the 71321LA55J8 datasheet, 71321LA55J8 pinout, 71321LA55J8 application, or 71321LA55J8 equivalent, key selection considerations include its MASTER-only BUSY output capability, 52-pin STQFP package, 5 V ±10% TTL-compatible supply, low 1 mW standby power, and interrupt mailbox addressing at 7FEh/7FFh.

Technical Context

The 71321LA55J8 implements on-chip port arbitration logic that asserts BUSYL/BUSYR outputs when address contention occurs between ports - based solely on CE and address timing, independent of R/W state. Its interrupt logic uses dedicated SRAM addresses (7FEh for INTL, 7FFh for INTR) to signal cross-port events without software polling.

As a MASTER-only device, it features open-drain BUSY outputs requiring 270 Ω pull-up resistors, while SLAVE devices (e.g., 71421LA) accept BUSY as an input to inhibit writes. The LA variant enables battery backup operation at 2 V with ≤100 µA retention current, distinguishing it from SA versions.

Key Specifications

Pinout & Package

71321LA55J8 is housed in a 52-pin STQFP (PPG52) package with 0.5 mm pitch, 10 mm × 10 mm body, and exposed thermal pad. Pin functions are symmetric for left/right ports, with dedicated interrupt and BUSY signaling lines.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual-port SRAM applications.

Compared with 71321LA35J8, the 71321LA55J8 trades 20 ns slower timing for broader industrial temperature compliance and higher noise immunity margins; compared with 71421LA55J8, it provides autonomous arbitration and interrupt generation - essential for single-device dual-processor interfaces.

Availability

71321LA55J8 is available at Aetrix Electronics and suitable for real-time industrial PLCs, avionics data concentrators, and railway signaling interlockers requiring stable component supply across extended product lifecycles.

Supply support for 71321LA55J8 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

IDT (Integrated Device Technology), now part of Renesas Electronics, is a fabless semiconductor company specializing in high-performance memory, timing, and interface solutions for communications and industrial markets.

The 71321LA55J8 belongs to IDT's dual-port SRAM product line, engineered specifically for deterministic interprocessor communication in safety-critical and real-time embedded systems where software-managed shared memory introduces unacceptable latency or complexity.

FAQ

What is the function of BUSYL and BUSYR on the 71321LA55J8?

On the 71321LA55J8, BUSYL and BUSYR are open-drain output flags indicating address contention between ports. When asserted (pulled low), they inhibit writes to the respective port. Each requires a 270 Ω external pull-up resistor to VCC. These signals are exclusive to the MASTER device and are not present as outputs on SLAVE variants like 71421LA55J8.

Does the 71321LA55J8 support battery backup operation?

Yes, the 71321LA55J8 supports battery backup with guaranteed data retention down to 2.0 V. In this mode, it draws ≤100 µA typical current (ICCDR) while preserving memory contents - a feature unique to LA-grade parts and not available in SA versions. This enables seamless operation during main power interruption in industrial and transportation systems.

Can the 71321LA55J8 be used as a SLAVE device in a width-expanded memory array?

No, the 71321LA55J8 is exclusively a MASTER device. It contains on-chip arbitration logic and outputs BUSY signals - functionality absent in SLAVE-only parts like 71421LA55J8. Attempting to use 71321LA55J8 as a SLAVE will cause incorrect BUSY behavior and potential data corruption. For width expansion, pair it only with genuine SLAVE devices.

How do the interrupt mailboxes at 7FEh and 7FFh work in the 71321LA55J8?

The 71321LA55J8 uses address 7FEh (hex) to set the left-port interrupt flag (INTL) when written by the right port, and 7FFh to set the right-port flag (INTR) when written by the left port. Reading those addresses clears the corresponding flag. These locations behave as standard SRAM bytes when interrupts are unused - no reserved memory overhead is incurred.

What package type is used for the 71321LA55J8, and are there thermal considerations?

The 71321LA55J8 uses a 52-pin STQFP (PPG52) package measuring 10 mm × 10 mm with 0.5 mm pitch and an exposed thermal pad. The pad must be soldered to a PCB thermal plane for reliable operation at full industrial temperature range. Thermal resistance (θJA) is 42°C/W typical; derating is required above 70°C ambient if power dissipation exceeds 250 mW.