Renesas 71421SA20PF8

Overview

71421SA20PF8 from IDT (now Renesas) is a high-speed 2K × 8 dual-port static RAM configured as a SLAVE device in MASTER/SLAVE memory expansion systems, supporting fully asynchronous port-to-port access with interrupt and BUSY arbitration logic. It delivers 20 ns read cycle time (max), operates on single 5V ±10% supply, and features TTL-compatible I/Os with industrial temperature range (–40°C to +85°C). It is used in real-time interprocessor communication buffers for embedded control systems requiring deterministic data exchange between independent CPUs.

For engineers reviewing the 71421SA20PF8 datasheet, 71421SA20PF8 pinout, 71421SA20PF8 application, or 71421SA20PF8 equivalent, key selection considerations include its role as SLAVE-only (no internal arbitration logic), BUSY input behavior, interrupt mailbox addressing (7FF_H/7FE_H), 52-pin PLCC package, and compatibility with IDT71321SA20PF8 MASTER devices in 16-bit+ bus width designs.

Technical Context

The 71421SA20PF8 implements a true dual-port SRAM architecture with physically separate left/right address, control, and bidirectional I/O buses - enabling concurrent read/write operations without internal contention detection. Unlike the MASTER IDT71321, it lacks on-chip arbitration logic and instead receives BUSY as an input signal to inhibit writes during address collisions.

Its interrupt functionality uses dedicated memory-mapped mailboxes: writing to address 7FF_H from the left port asserts INTR (right port flag), while writing to 7FE_H asserts INTL (left port flag); flags are cleared by reading those same addresses. All timing parameters - including tINS (20 ns max interrupt set time), tINR (20 ns max reset time), and tWB (0 ns write-to-BUSY input delay) - are specified for commercial-grade operation at 20 ns speed grade.

Key Specifications

Pinout & Package

71421SA20PF8 is packaged in a 52-pin Plastic Leaded Chip Carrier (PLCC), body size ≈ 19.05 mm × 19.05 mm × 4.32 mm, with J-lead configuration and moisture sensitivity level (MSL) 3 per JEDEC J-STD-020. Pin 1 is marked by corner notch; pins are numbered counter-clockwise starting from top-left.

Key Features

Applications

Equivalent & Alternatives

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

Compared with IDT71321SA20PF8 and CY7C136-20VC, the 71421SA20PF8 uniquely provides SLAVE-specific BUSY input behavior and fixed-function interrupt mailboxes - making it irreplaceable in IDT-optimized MASTER/SLAVE architectures where deterministic hardware arbitration is mandatory.

Availability

71421SA20PF8 is available at Aetrix Electronics and suitable for real-time motion control, dual-core industrial PLCs, avionics data concentrators, and medical imaging subsystems requiring stable component supply and long-term obsolescence management.

Supply support for 71421SA20PF8 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, RF, and high-performance data conversion ICs for communications, computing, and industrial markets.

The IDT71321/71421 product line was designed specifically for deterministic interprocessor communication in hard real-time embedded systems - emphasizing hardware-enforced arbitration, low-latency interrupt signaling, and seamless bus-width expansion without external logic.

FAQ

Is 71421SA20PF8 pin-compatible with IDT71321SA20PF8?

No. Although both share the same 52-pin PLCC package and core signal names, 71421SA20PF8 has BUSYL/BUSYR as inputs, whereas IDT71321SA20PF8 drives them as open-drain outputs. Swapping them causes functional failure due to reversed BUSY signal direction and missing arbitration logic in the 71421SA20PF8.

What is the function of address 7FF_H in 71421SA20PF8?

In 71421SA20PF8, writing to address 7FF_H from the left port asserts the INTR flag (right port interrupt), signaling new data arrival. Reading 7FF_H from the right port clears INTR. This location serves as a hardware-managed mailbox - no configuration registers or initialization is required to enable this behavior in the 71421SA20PF8.

Does 71421SA20PF8 support battery backup or low-voltage data retention?

No. The 'SA' suffix denotes standard active power consumption and excludes battery backup capability. Only LA-suffix variants (e.g., 71421LA20PF8) support 2V data retention. The 71421SA20PF8 requires continuous 5V supply for memory retention - loss of VCC results in immediate data loss.

Can 71421SA20PF8 operate as a standalone dual-port RAM without a MASTER device?

Yes, but with critical limitations: BUSY pins must be held HIGH (e.g., via pull-up resistors) since they are inputs and cannot be left floating, and interrupt flags require external coordination as there is no internal arbitration to resolve simultaneous accesses. Full functionality - especially deterministic contention handling - requires pairing with IDT71321SA20PF8 as MASTER.

What is the maximum operating frequency implied by the 20 ns access time of 71421SA20PF8?

The 20 ns tRC (read cycle time) specifies the minimum interval between successive read operations on the same port. It does not define a clock frequency - the 71421SA20PF8 is fully asynchronous and has no internal clock. System-level throughput depends on address/control setup/hold times and bus turnaround; sustained 50 MHz burst reads are achievable under optimal timing conditions.