Renesas 71321SA20TF8

Overview

71321SA20TF8 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 20 ns max read cycle time, operates on single 5V ±10% supply, and features open-drain BUSY/INT outputs requiring 270 Ω pull-up resistors. It is used in real-time embedded systems where two CPUs share memory without software coordination - e.g., DSP + microcontroller co-processing in industrial motion controllers.

For engineers reviewing the 71321SA20TF8 datasheet, 71321SA20TF8 pinout, 71321SA20TF8 application, or 71321SA20TF8 equivalent, key selection criteria include its MASTER-only arbitration logic, 20 ns access timing, 52-pin STQFP package, and dual-interrupt mailbox addressing (7FEh/7FFh), all critical for deterministic port-to-port handshaking in safety-critical control loops.

Technical Context

The 71321SA20TF8 implements fully asynchronous dual-port operation with independent left/right address, control, and I/O buses. Its on-chip arbitration logic monitors CE and address signals (not R/W state) to assert BUSYL/BUSYR outputs when both ports access the same address, preventing write contention.

Interrupt functionality uses dedicated mailbox addresses: writing to 7FEh sets INTL (left port flag), writing to 7FFh sets INTR (right port flag); clearing is performed by reading those same locations with OE enabled. The device requires external 270 Ω pull-ups on BUSY and INT pins due to open-drain output structure.

Key Specifications

Pinout & Package

71321SA20TF8 is packaged in a 52-pin STQFP (PPG52), measuring 10 mm × 10 mm × 1.4 mm, with exposed pad for thermal dissipation. Pin 1 is located at bottom-left corner (marking dot adjacent), and all VCC (pins 18, 27, 39, 46) and GND (pins 26, 33, 40, 47) must be individually decoupled.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CY7C024AV-20AXC and IDT71421SA20TF8, the 71321SA20TF8 uniquely integrates MASTER arbitration and interrupt mailboxes in a 5V-compatible 2K × 8 form factor - making it irreplaceable in deterministic, low-latency interprocessor communication where hardware-enforced exclusivity is mandatory.

Availability

71321SA20TF8 is available at Aetrix Electronics and suitable for industrial motion controllers, avionics data acquisition units, redundant safety PLCs, and DSP+MCU co-processing platforms requiring stable component supply across extended production lifecycles.

Supply support for 71321SA20TF8 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, is a fabless semiconductor company specializing in timing, memory interface, and RF power solutions for high-performance computing and communications infrastructure.

The 71321SA20TF8 belongs to IDT's legacy dual-port SRAM product line, engineered specifically for deterministic interprocessor communication in real-time embedded systems where hardware arbitration and interrupt signaling eliminate software overhead and timing uncertainty.

FAQ

What is the function of the BUSY pins on the 71321SA20TF8?

The BUSYL and BUSYR pins on the 71321SA20TF8 are open-drain outputs that assert low when both ports attempt to access the same memory address simultaneously. This hardware signal blocks writes on the contending port, preventing data corruption. Because they are open-drain, each BUSY pin requires an external 270 Ω pull-up resistor to VCC to ensure proper logic-high idle state. The 71321SA20TF8 implements this arbitration solely based on CE and address timing - not R/W state - ensuring deterministic behavior even during mixed read/write operations.

How do the interrupt mailboxes work in the 71321SA20TF8?

The 71321SA20TF8 uses fixed memory-mapped interrupt mailboxes: writing any data to address 7FEh (hex) asserts the INTL flag (left port), and writing to 7FFh asserts the INTR flag (right port). Clearing is performed by reading those same addresses with OE enabled. These locations remain fully accessible as regular SRAM when interrupts are unused. The 71321SA20TF8 guarantees atomic flag setting without software intervention, enabling lock-free, low-latency interprocessor signaling essential for hard real-time systems.

Can the 71321SA20TF8 operate with a 3.3V supply?

No, the 71321SA20TF8 is specified exclusively for 5V ±10% operation (4.5 V to 5.5 V). Its input thresholds (VIH = 2.2 V min, VIL = 0.8 V max) and output drive strength are optimized for TTL/5V CMOS compatibility. Applying 3.3V violates the Absolute Maximum Ratings and will result in undefined logic states, excessive leakage, or permanent damage. For 3.3V systems, consider newer alternatives like the Renesas IS61WV20488BLL-10TLI, but note it lacks integrated BUSY arbitration and interrupt mailboxes found in the 71321SA20TF8.

What package type does the 71321SA20TF8 use, and what are its board layout requirements?

The 71321SA20TF8 uses a 52-pin STQFP (PPG52) package measuring 10 mm × 10 mm × 1.4 mm with an exposed thermal pad. Layout requires connecting all four VCC pins (18, 27, 39, 46) and all four GND pins (26, 33, 40, 47) to dedicated planes, each with ≥0.1 µF ceramic decoupling placed within 3 mm of the pin. The exposed pad must be soldered to a solid copper thermal pad tied to internal ground plane via ≥4 thermal vias (0.3 mm diameter) to ensure reliable thermal performance under continuous 325 mW operation.

Is the 71321SA20TF8 pin-compatible with the IDT71421SA20TF8?

No - although both share the same 52-pin STQFP package and identical pinout numbering, the 71321SA20TF8 and IDT71421SA20TF8 have fundamentally different internal functions. The 71321SA20TF8 is a MASTER with BUSY outputs and on-chip arbitration logic; the IDT71421SA20TF8 is a SLAVE with BUSY inputs and no arbitration. Swapping them electrically connects outputs to inputs incorrectly, causing bus contention and system failure. They are complementary, not interchangeable. The 71321SA20TF8 must be used as the MASTER in any master/slave configuration.