Infineon Technologies CY7C421-20VXC

Overview

CY7C421-20VXC 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, TTL-compatible I/O, and standalone/expandable operation supporting width or depth cascading. It serves as a data buffering interface between mismatched-speed digital subsystems in communication controllers and industrial PLCs.

For engineers reviewing the CY7C421-20VXC datasheet, CY7C421-20VXC pinout, CY7C421-20VXC application, or CY7C421-20VXC equivalent, key selection criteria include access time (20 ns), FIFO depth/width (512 × 9), flag behavior (EF/FF/HF), retransmit capability, and PLCC-32/TQFP-32 package compatibility.

Technical Context

The CY7C421-20VXC implements an asynchronous dual-port RAM core with independent read and write address pointers, enabling concurrent data ingestion and egress without shared clock domain constraints. Its expansion logic supports unlimited width or depth stacking via XI/XO signals and FL control for first-load sequencing.

Flag generation is synchronous to respective control edges: EF asserts low after final read empties the buffer; FF goes low on write attempt to full buffer; HF provides half-full status in standalone mode or expansion-out signaling in depth-cascaded configurations. Retransmit mode requires simultaneous R and W high before R-triggered replay.

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-018AC compliant. Also available in 32-pin TQFP and 28-pin DIP variants.

Key Features

Applications

Equivalent & Alternatives

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

Compared with IDT7201L20J and AM7201-20JC, the CY7C421-20VXC offers unique retransmit functionality and guaranteed industrial temperature support, while maintaining pin compatibility and identical 20 ns timing-making it the preferred choice for new designs requiring robust retry capability.

Availability

CY7C421-20VXC is available at Aetrix Electronics and suitable for industrial PLCs, legacy bus bridges, RS-485 Modbus nodes, and video timing alignment circuits requiring stable component supply and long-lifecycle support.

Supply support for CY7C421-20VXC 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) is a U.S.-based semiconductor company specializing in programmable system-on-chip solutions, memory, and interface ICs for industrial, automotive, and consumer applications.

The CY7C421 belongs to Cypress's legacy asynchronous FIFO product line, designed specifically for deterministic data buffering between unsynchronized digital subsystems in real-time control and communications equipment.

FAQ

What is the purpose of the FL/RT pin in different configurations?

The FL/RT pin serves dual roles: in width expansion mode, it acts as First Load (FL) and must be tied HIGH on the master device to synchronize parallel FIFO initialization; in standalone mode, it functions as Retransmit (RT), and a LOW pulse triggers replay of the most recently read data word while R and W remain HIGH-enabling hardware-level protocol retries without CPU involvement.

How does the XO/HF pin behave in depth expansion versus standalone operation?

In standalone or width expansion, XO/HF outputs a LOW signal when exactly 256 words are stored (half-full condition); in depth expansion, it becomes Expansion Out (XO), asserting LOW to enable the downstream FIFO only after the upstream device reaches full capacity-ensuring atomic buffer chaining without intermediate flag arbitration.

Can CY7C421-20VXC operate reliably at 50 MHz with 20 ns access time?

Yes-the 20 ns access time (tA) and 30 ns minimum read cycle time (tRC) are specified under worst-case industrial conditions (–40°C to +85°C, VCC = 4.5 V). At 50 MHz (20 ns period), timing margins are maintained because tRC defines the minimum interval between successive R pulses, not the access delay itself-allowing sustained 50 MHz operation with proper setup/hold compliance.

Is the CY7C421-20VXC compatible with 3.3 V logic interfaces?

No-it requires 5 V ±10% supply and features TTL-compatible input thresholds (VIH ≥ 2.0 V), making it incompatible with pure 3.3 V CMOS logic without level translation. Driving inputs from 3.3 V sources risks marginal VIH margin; receiving outputs into 3.3 V inputs may exceed absolute maximum ratings due to 5 V swing-external buffers or resistive dividers are required for safe interfacing.