Renesas 71321SA55PF8

Overview

71321SA55PF8 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 delivers 55 ns max read/write cycle time, operates on single 5V ±10% supply, supports industrial temperature range (–40°C to +85°C), and features open-drain BUSY/INT outputs requiring 270 Ω pull-up resistors - used in real-time embedded control systems requiring concurrent CPU/DSP memory access.

For engineers reviewing the 71321SA55PF8 datasheet, 71321SA55PF8 pinout, 71321SA55PF8 application, or 71321SA55PF8 equivalent, key selection criteria include its MASTER arbitration capability, 55 ns timing grade, 64-pin TQFP package, battery-backed data retention (not supported - LA variant only), and compatibility with IDT71421SLAVE devices for 16-bit+ width expansion.

Technical Context

The 71321SA55PF8 implements fully asynchronous dual-port operation with independent left/right address, control, and I/O buses. Its on-chip arbitration logic resolves port contention via BUSY flag generation based on chip enable (CEL/CER) and address match detection - not R/W state - ensuring deterministic write inhibition during simultaneous access to identical addresses.

Interrupt functionality uses dedicated mailbox addresses (7FE_H for INTL, 7FF_H for INTR) with edge-triggered flag assertion and software-clearing via read/write to those locations. All I/Os are TTL-compatible; BUSY and INT pins are open-drain outputs requiring external 270 Ω pull-up resistors per datasheet Figure 3.

Key Specifications

Pinout & Package

71321SA55PF8 is packaged in a 64-pin TQFP (PNG64) with 0.5 mm pitch, body size 14 mm × 14 mm × 1.4 mm. Pin functions are defined per datasheet drawing 2691 drw 03.

Key Features

Applications

Equivalent & Alternatives

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

Compared with IDT71421SA55PF8 and CY7C024AV-55AXC, the 71321SA55PF8 uniquely integrates MASTER arbitration, dual interrupt mailboxes, and 5V TTL compatibility - enabling simpler, lower-latency interprocessor designs without external glue logic.

Availability

71321SA55PF8 is available at Aetrix Electronics and suitable for industrial PLC controllers, avionics data concentrators, and medical imaging systems requiring stable component supply, long-term lifecycle support, and guaranteed industrial temperature performance.

Supply support for 71321SA55PF8 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, specializes in high-performance timing, memory, and interface solutions for real-time embedded systems.

The IDT71321 family was engineered specifically for deterministic interprocessor communication in dual-CPU, CPU-DSP, and safety-critical control architectures - prioritizing hardware arbitration, interrupt offload, and industrial reliability over density or voltage scaling.

FAQ

What is the function of the BUSY pin on the 71321SA55PF8?

The BUSY pin on the 71321SA55PF8 is an open-drain output that asserts LOW when port contention occurs - i.e., when both left and right ports attempt access to the same memory address simultaneously. It requires a 270 Ω external pull-up resistor per datasheet Figure 3. This signal is used to inhibit writes on the contending port, ensuring data integrity without software intervention. The 71321SA55PF8 implements this as a MASTER device, unlike SLAVE variants where BUSY is an input.

Does the 71321SA55PF8 support battery backup data retention?

No, the 71321SA55PF8 does not support battery backup data retention. That feature is exclusive to the LA variant (e.g., 71321LA55PF8), which guarantees data retention at VCC = 2.0 V. The 'SA' suffix denotes standard active power consumption (325 mW typ.), while 'LA' indicates low-power design with 2V retention capability. Using 71321SA55PF8 in battery-backed systems will result in data loss below 4.5 V.

Can the 71321SA55PF8 be used as a standalone dual-port RAM without a SLAVE device?

Yes, the 71321SA55PF8 functions fully as a standalone 2K × 8 dual-port SRAM. Its MASTER arbitration logic operates internally - BUSY generation and interrupt flagging require no external SLAVE. The SLAVE pairing (e.g., with IDT71421) is optional and only needed for memory width expansion beyond 8 bits. Standalone use is common in dual-processor systems where both sides access the full 2K × 8 space independently.

What are the valid interrupt mailbox addresses for the 71321SA55PF8?

The 71321SA55PF8 uses two fixed SRAM addresses for hardware interrupt signaling: address 7FE_H (2046 decimal) sets the left-port interrupt flag (INTL), and address 7FF_H (2047 decimal) sets the right-port interrupt flag (INTR). Writing any data to these locations with the corresponding port's CE and R/W asserted LOW triggers the respective open-drain flag. Reading from these addresses clears the flag - no dedicated control register is involved.

Is the 71321SA55PF8 pin-compatible with faster or slower speed grades like 71321SA35PF8?

Yes, all speed grades of the 71321SAxxPF8 (20 ns, 35 ns, 55 ns) share identical 64-pin TQFP (PNG64) packaging and pinout - including power, ground, address, data, and control signals. Timing parameters differ (e.g., tRC = 55 ns max for 71321SA55PF8 vs. 35 ns for 71321SA35PF8), but electrical interface and PCB layout are fully interchangeable. Slower grades may be substituted in designs where timing margin permits, but not vice versa.