Renesas 71421SA25J

Overview

71421SA25J from Integrated Device Technology is a 2K × 8 dual-port static RAM configured as a SLAVE device in MASTER/SLAVE memory expansion systems, supporting fully asynchronous port-to-port communication with BUSY input and interrupt flags (INTL/INTR). It delivers 25 ns max read cycle time, operates on single 5V ±10% supply, and targets industrial temperature range (–40°C to +85°C) for real-time interprocessor data exchange.

For engineers reviewing the 71421SA25J datasheet, 71421SA25J pinout, 71421SA25J application, or 71421SA25J equivalent, key selection criteria include its role as SLAVE in width-expanded 16-bit+ memory systems, BUSY input behavior (not output), interrupt mailbox addressing (7FEH/7FFH), and compatibility with IDT71321SA25J MASTER devices in shared-address configurations.

Technical Context

The 71421SA25J implements dedicated SLAVE functionality: BUSY pin is an input (not open-drain output), used to inhibit writes during address contention when driven by a MASTER IDT71321; it lacks on-chip arbitration logic and relies entirely on external BUSY assertion from the MASTER device.

It supports two independent TTL-compatible ports (left/right), each with separate CE/OE/R/W controls, 11-bit address bus (A0–A10), and 8-bit bidirectional I/O (I/O0–I/O7); interrupt generation is triggered only by writes to fixed mailbox addresses (7FEH for INTL, 7FFH for INTR), with no internal arbitration priority setup timing (tAPS not applicable).

Key Specifications

Pinout & Package

71421SA25J is packaged in 52-pin STQFP (PPG52), measuring 10 mm × 10 mm × 1.4 mm, with exposed thermal pad (not electrically connected). All VCC pins require local 0.1 µF decoupling; all GND pins must be solidly tied to ground plane.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CY7C136-25JC, 71421SA25J offers integrated interrupt mailboxes and native SLAVE BUSY input behavior, reducing BOM count and firmware complexity; versus IDT71321SA25J, it eliminates arbitration logic overhead but requires pairing with a MASTER for full contention resolution.

Availability

71421SA25J is available at Aetrix Electronics and suitable for real-time interprocessor communication, redundant control system memory, and industrial PLC dual-port data exchange requiring stable component supply, long-term lifecycle support, and guaranteed industrial temperature performance.

Supply support for 71421SA25J 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

Integrated Device Technology (IDT), now part of Renesas Electronics, designs high-performance timing, memory, and interface solutions for communications, computing, and industrial markets.

The IDT71321/71421 family was engineered specifically for deterministic, low-latency interprocessor memory sharing in embedded control systems - prioritizing hardware arbitration, interrupt signaling, and industrial environmental robustness over general-purpose SRAM features.

FAQ

What is the function of BUSY pins on the 71421SA25J?

The BUSYL and BUSYR pins on the 71421SA25J are inputs - not outputs - and must be driven LOW by an external MASTER device (e.g., IDT71321SA25J) to inhibit writes during address contention. Unlike the MASTER, the 71421SA25J contains no internal arbitration logic and relies entirely on this external BUSY signal to ensure atomic memory updates. Pull-up resistors are not required on these pins.

Can the 71421SA25J operate as a standalone dual-port RAM without a MASTER device?

Yes, the 71421SA25J can operate as a standalone dual-port RAM, but only in non-contention scenarios where left and right ports never access the same address simultaneously. In such cases, BUSYL and BUSYR must be held HIGH (e.g., via pull-up) to enable writes. However, for guaranteed contention resolution and deterministic behavior, it must be paired with an IDT71321SA25J MASTER in width-expanded systems.

How do the interrupt flags INTL and INTR work on the 71421SA25J?

INTL is asserted (open-drain LOW) when the right port writes to address 7FEH; INTR is asserted when the left port writes to 7FFH. Both flags remain active until the respective port performs a read or write to that same address. The 71421SA25J treats these as standard SRAM locations - no special register mapping is required. Pull-up resistors of 270 Ω are mandatory for proper flag voltage levels.

What package and pin count does the 71421SA25J use?

The 71421SA25J uses a 52-pin STQFP package (PPG52), measuring 10 mm × 10 mm × 1.4 mm with an exposed thermal pad. Pinout matches the IDT71321SA25J in all signal positions, enabling drop-in PCB layout reuse when designing MASTER/SLAVE pairs - though BUSY pin function differs (input vs. output), requiring trace routing adjustment.

Is battery backup supported on the 71421SA25J?

No, battery backup and 2V data retention are exclusive to LA-suffix variants (e.g., 71421LA25J). The 71421SA25J is the standard-power version, optimized for active operation with typical active current of 110 mA and standby current of 30 mA. For battery-backed applications, the LA variant must be selected and properly biased per datasheet Section 5.