AMD XC18V256PC20C

Overview

XC18V256PC20C from Xilinx is a 256-Kbit in-system programmable configuration PROM designed to store and deliver FPGA bitstreams in Master Serial, Slave Serial, or Slave-Parallel/SelectMAP modes. It features 20,000 program/erase cycles, IEEE 1149.1 JTAG compliance, 5V-tolerant I/Os, 3.3V core supply, and PC20 (20-pin PLCC) packaging. It is used in Xilinx Spartan-II, Virtex, and Virtex-E FPGA configuration systems requiring field-upgradable nonvolatile storage.

For engineers reviewing the XC18V256PC20C datasheet, pinout, applications, or equivalent options, key selection considerations include serial vs. parallel configuration bandwidth (up to 33 MHz), JTAG-initiated CONFIG pulse timing (300–500 ns), 5V-tolerant input compatibility, dual VCC/VCCO supply support, and cascading capability via CEO/CE chaining for multi-FPGA or large-bitstream deployments.

Technical Context

The XC18V256PC20C implements a flash-based memory array with boundary-scan TAP controller supporting IEEE 1149.1 mandatory and optional instructions-including CONFIG, IDCODE, and USERCODE. Its internal address counter increments on each rising CLK edge when CE=Low and OE/RESET=High, enabling synchronous data delivery aligned to FPGA CCLK.

Configuration mode selection (serial vs. parallel) is controlled via a user-accessible JTAG register setting-not hardware pins-and defaults to serial mode. The CF pin (routed to D4 in 20-pin packages) provides JTAG-triggered FPGA reset and configuration initiation, requiring connection to the FPGA PROGRAM pin.

Key Specifications

Pinout & Package

XC18V256PC20C is housed in a 20-pin plastic leaded chip carrier (PC20, PLCC-20) package with gull-wing leads, compatible with standard PLCC sockets and reflow soldering. Pin 1 is marked by a corner notch; pin numbering proceeds counterclockwise.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar configuration PROM applications.

Compared with XC18V256SO20C, the XC18V256PC20C offers socket-based reworkability and higher vibration resistance; compared with XC17V256PC20C, it adds field-upgrade capability at the cost of slightly higher unit price and programming infrastructure requirements.

Availability

XC18V256PC20C is available at Aetrix Electronics and suitable for industrial PLCs, telecom baseband systems, aerospace avionics, automated test equipment, and FPGA-based prototyping platforms requiring stable component supply across extended product lifecycles.

Supply support for XC18V256PC20C 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

Xilinx, now part of AMD, is a pioneer in programmable logic and FPGA technology, with decades of leadership in configurable silicon for high-performance digital systems.

The XC18V00 series was engineered specifically to provide in-system reprogrammable, nonvolatile configuration storage for Xilinx FPGAs-enabling rapid design iteration, field upgrades, and secure bitstream deployment without external microcontrollers or complex boot loaders.

FAQ

What configuration modes does the XC18V256PC20C support?

The XC18V256PC20C supports serial (Master/Slave) and parallel (Slave-Parallel/SelectMAP) configuration modes. Mode selection is performed via a JTAG-accessible control register using Xilinx iMPACT software-not hardware strapping. Serial mode is default; parallel mode must be explicitly enabled. Both modes operate up to 33 MHz, with parallel delivering 8-bit data per clock cycle for faster FPGA startup. The XC18V256PC20C does not support master parallel mode.

How is the CF function implemented on the 20-pin PC20 package of XC18V256PC20C?

In the XC18V256PC20C's 20-pin PLCC package, there is no dedicated CF pin. Instead, the CF (CONFIG) function is routed to pin 7-normally D4-when the CF→D4 programming option is enabled during configuration file generation in Xilinx iMPACT. This routing is only valid if parallel mode is disabled; using D4 as CF precludes 8-bit parallel output. The CF pulse duration is 300–500 ns and is triggered exclusively via the JTAG CONFIG instruction.

Can XC18V256PC20C be used with modern Xilinx FPGA families like Artix or Kintex?

No-XC18V256PC20C is designed exclusively for legacy Xilinx FPGA families including Spartan-II, Spartan-IIE, Virtex, Virtex-E, and early Virtex-II devices. It is not compatible with 7-series (Artix-7, Kintex-7), UltraScale, or Versal FPGAs, which require different configuration protocols (e.g., SPIx4, BPI, or fallback modes) and lack native support for XC18V00-style serial/parallel PROM interfaces. Migration requires redesigning the configuration subsystem.

What is the role of CEO and how is it used in cascaded configurations?

The CEO (Chip Enable Output) of XC18V256PC20C is an open-drain output that goes low after the internal address counter reaches terminal count (TC), signaling end-of-data. In cascaded setups, CEO from the first PROM drives the CE input of the second, enabling its DATA outputs only after the first PROM completes transmission. This allows seamless chaining of multiple XC18V256PC20C devices to store larger bitstreams or configure multiple FPGAs. Each device requires its own VCC, VCCO, and GND connections; CLK and DATA lines are shared across the chain.

Does XC18V256PC20C support read protection, and how is it configured?

Yes-XC18V256PC256PC20C supports JTAG read security via a user-settable read security bit. When enabled, it inhibits reading of the internal configuration array through JTAG (IDCODE and USERCODE remain readable). The bit is set during programming using Xilinx iMPACT's "Security Bit" option. Once set, the only way to clear it is to perform a full device erase-which also clears all stored configuration data. This feature protects intellectual property in deployed systems where physical access to the JTAG port may exist.