Renesas 71321SA55J8

Overview

71321SA55J8 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. It supports 55 ns max access time, TTL-compatible 5V ±10% supply, industrial temperature range (–40°C to +85°C), and operates with active power of 110 mA (typ.) and standby current as low as 1.0 mA (full CMOS standby). It is used in real-time embedded systems requiring concurrent read/write access between two processors or buses.

For engineers reviewing the 71321SA55J8 datasheet, 71321SA55J8 pinout, 71321SA55J8 application, or 71321SA55J8 equivalent, this page delivers verified technical context, package mapping, interrupt timing behavior, BUSY arbitration constraints, and validated alternative parts - all grounded in the official IDT DSC-2691/17 datasheet (September 2019).

Technical Context

The 71321SA55J8 implements fully asynchronous dual-port architecture with independent left/right address, control, and I/O buses. Its on-chip arbitration logic resolves port contention via BUSY flag generation based solely on chip enable (CEL/CER) and address match - not R/W state - enabling deterministic write inhibition during simultaneous access to identical addresses.

As a MASTER device, it features open-drain BUSYL/BUSYR outputs (requiring 270 Ω pull-up) and internal INTL/INTR flag generation triggered by writes to dedicated mailbox addresses (7FEh/7FFh). It does not support battery backup - that function is exclusive to LA variants - and requires external pull-ups for BUSY/INT signals per datasheet Note 1 and Figure 3.

Key Specifications

Pinout & Package

71321SA55J8 is packaged in 52-pin STQFP (PPG52), measuring 10 mm × 10 mm × 1.4 mm. Pin assignments are defined in datasheet Figure 03a (PPG52 top view) and confirmed across Tables 12–14 and Waveforms 10–15.

Key Features

Applications

Equivalent & Alternatives

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

Compared with IDT71421SA55J8 and CY7C024AV-55AXC, the 71321SA55J8 uniquely integrates MASTER arbitration, open-drain BUSY outputs with defined pull-up requirement, and fixed 7FEh/7FFh mailbox addressing - making it irreplaceable in standalone or MASTER-led dual-processor systems requiring hardware-enforced coherency.

Availability

71321SA55J8 is available at Aetrix Electronics and suitable for industrial PLC communication modules, military avionics data buffers, and telecom line card buffers requiring stable component supply, long-term lifecycle support, and guaranteed industrial temperature performance.

Supply support for 71321SA55J8 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, specialized in high-performance timing, memory, and interface ICs for communications, computing, and industrial markets.

The IDT71321 family was designed specifically for deterministic interprocessor communication in real-time embedded systems - emphasizing hardware arbitration, interrupt-driven messaging, and seamless width expansion without performance penalty.

FAQ

What is the function of the BUSY pins on the 71321SA55J8?

The BUSYL and BUSYR pins on the 71321SA55J8 are open-drain arbitration outputs that assert LOW when address contention occurs between ports - i.e., when both ports attempt access to the same memory location. As specified in datasheet Note 1, they require external 270 Ω pull-up resistors to VCC. The 71321SA55J8 uses these signals to internally inhibit writes during conflict, ensuring data integrity without software intervention.

Does the 71321SA55J8 support battery backup operation?

No, the 71321SA55J8 does not support battery backup. Battery-backed data retention (down to 2 V) is exclusive to LA-suffixed variants such as IDT71321LA55J8, as confirmed in Table 06 (Data Retention Characteristics) and Feature list section "Battery backup operation – 2V data retention (LA only)". The 71321SA55J8 is an SA-series part optimized for speed and industrial temperature, not low-voltage retention.

How are interrupts generated and cleared in the 71321SA55J8?

In the 71321SA55J8, INTL is asserted when the right port writes to address 7FEh, and INTR is asserted when the left port writes to 7FFh - per Truth Table II. To clear INTL, the left port must perform a read or write to 7FEh with CEL = OEL = VIL; to clear INTR, the right port accesses 7FFh under CER = OER = VIL. These mailbox addresses are fixed and hardware-decoded - no configuration registers are involved.

Can the 71321SA55J8 be used without external pull-up resistors on BUSY and INT pins?

No. The 71321SA55J8's BUSYL, BUSYR, INTL, and INTR pins are open-drain outputs, as explicitly stated in datasheet Notes 1 and 2 and Figure 3. Without 270 Ω pull-up resistors to VCC, these signals cannot drive a valid HIGH logic level, causing arbitration failure and unreliable interrupt signaling. This requirement is non-negotiable and applies to all operating conditions.

What is the difference between the 71321SA55J8 and 71421SA55J8?

The 71321SA55J8 is the MASTER dual-port SRAM with on-chip arbitration logic, open-drain BUSY outputs, and interrupt generation capability. The 71421SA55J8 is the SLAVE variant: BUSY pins are inputs (not outputs), it lacks arbitration logic, and it relies on the MASTER's BUSY signal to inhibit writes. Both share identical speed (55 ns), voltage (5V), and package (PPG52), but only the 71321SA55J8 can operate stand-alone as a MASTER.