Infineon Technologies CY7C421-20JXI

Overview

CY7C421-20JXI from Cypress Semiconductor is a 512 × 9 asynchronous FIFO memory IC with dual-port RAM architecture, 20 ns access time, 50 MHz max read/write clock rate, and TTL-compatible I/O. It provides independent read/write control via W/R signals, EF/FF/HF flags, and retransmit capability-used in data buffering between mismatched clock domains in industrial serial gateways and legacy bus bridges.

For engineers reviewing the CY7C421-20JXI datasheet, CY7C421-20JXI pinout, CY7C421-20JXI application, or CY7C421-20JXI equivalent, key selection criteria include asynchronous depth expansion support, half-full flag behavior in standalone mode, retransmit timing constraints, and 32-pin PLCC package compatibility with legacy PCB footprints.

Technical Context

The CY7C421-20JXI implements a true dual-port RAM core with independent write and read address pointers, enabling concurrent read/write operations without arbitration logic. Its expansion architecture uses XI/XO pins to cascade devices in depth or width, with XO repurposed as HF in non-cascaded configurations.

Retransmit functionality requires simultaneous HIGH on R and W, then toggling R to replay the last-read word; MR resets both pointers and flags. The device operates at 5 V ±10% across commercial (0°C to +70°C) and industrial (–40°C to +85°C) temperature ranges with 35 mA typical ICC1 at 20 MHz.

Key Specifications

Pinout & Package

Package: 32-pin PLCC (Plastic Leaded Chip Carrier), 11.43 mm × 11.43 mm body, 1.27 mm pitch, JEDEC MS-026AC compliant.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar asynchronous FIFO applications.

Compared with IDT7201L20SOI and AM7201-20JC, the CY7C421-20JXI uniquely combines PLCC socket compatibility, retransmit functionality, and industrial temperature range support-making it optimal for field-deployed equipment requiring firmware-upgradeable error recovery and long-term mechanical serviceability.

Availability

CY7C421-20JXI is available at Aetrix Electronics and suitable for industrial serial gateways, legacy bus bridges, test equipment data capture, and avionics ARINC 429 interfaces requiring stable component supply across extended lifecycle programs.

Supply support for CY7C421-20JXI 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

Cypress Semiconductor (now part of Infineon Technologies) designs high-reliability memory and programmable logic solutions for industrial, automotive, and aerospace applications.

The CY7C421 belongs to Cypress's legacy asynchronous FIFO product line, engineered specifically for deterministic data buffering in mixed-clock-domain systems where metastability avoidance and flag-driven flow control are mandatory.

FAQ

What is the function of the FL/RT pin in standalone versus depth expansion mode?

In standalone mode, FL/RT acts as Retransmit (RT): a LOW pulse triggers replay of the last-read word while R and W remain HIGH. In depth expansion, FL is First Load: the first device in chain has FL grounded to indicate primary load position; all others tie FL to VCC. This pin cannot serve both roles simultaneously-the mode is determined by system-level interconnect topology.

Can CY7C421-20JXI operate reliably at 50 MHz with full 512-word depth?

Yes. The 50 MHz maximum clock rate is guaranteed across all depths and widths per datasheet specification. Access time remains fixed at 20 ns regardless of fill level because the dual-port RAM architecture uses independent address pointers-not shift-register or serial logic-ensuring constant latency from empty to full conditions.

How does the XO/HF pin behave in width expansion versus standalone configuration?

In standalone and width expansion modes, XO/HF functions as Half Full flag: LOW indicates exactly 256 words stored. In depth expansion, XO/HF becomes Expansion Out (XO), signaling activation to the next device in chain. The functional mode is determined solely by whether XI is connected to another device's XO (depth) or tied to VCC (standalone/width).

Is master reset (MR) synchronous or asynchronous, and what timing constraints apply?

MR is fully asynchronous: it immediately clears read/write pointers and forces EF=HIGH, FF=LOW, and HF=HIGH without waiting for clock edges. The minimum MR pulse width is 20 ns (per tPMR spec), and recovery time to valid flag states is 25–30 ns (tEFL/tHFH). No clock signal is required for reset assertion or release.