AMD XC18V256SO20C

Overview

XC18V256SO20C from Xilinx is a 262,144-bit (256 Kbit) in-system programmable 3.3V configuration PROM designed to store and serially/parallel load bitstreams into Xilinx FPGAs. It supports Master Serial, Slave Serial, Master-SelectMAP, and Slave-Parallel modes; features IEEE 1149.1 JTAG boundary-scan; offers 20,000 program/erase cycles; and uses a low-power advanced CMOS FLASH process. It is used in FPGA-based embedded control, industrial logic controllers, and reconfigurable communication interfaces.

For engineers reviewing the XC18V256SO20C datasheet, pinout, applications, or equivalent options, key selection criteria include its 256-Kbit capacity, SO20 package compatibility with Spartan-II/XC2S15 FPGAs, dual configuration mode support (serial up to 33 MHz / parallel up to 264 Mb/s), 5V-tolerant I/Os, and JTAG-initiated CONFIG functionality via CF pin.

Technical Context

The XC18V256SO20C implements a flash-based nonvolatile memory architecture with an internal address counter driven by CLK under CE Low and OE/RESET High conditions. Its JTAG TAP controller supports required instructions (BYPASS, SAMPLE/PRELOAD, EXTEST) and XC18V00-specific CONFIG instruction to pulse CF low for FPGA reset and configuration initiation.

It operates in two primary interface modes: serial (D0 only, 1-bit data path) and parallel (D0–D7, 8-bit data path), selectable via user control register programmed through JTAG. The device uses separate VCC (3.3V core) and VCCO (3.3V or 2.5V output drivers) supplies and maintains 5V tolerance on all I/O pins regardless of supply sequencing order.

Key Specifications

Pinout & Package

XC18V256SO20C is housed in a 20-pin Small Outline Integrated Circuit (SOIC) package with 0.300-inch body width and standard gull-wing lead form. Pin assignments are fixed per Xilinx DS026 v3.9 and validated for SO20 top-view orientation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with XC18V256PC20C and XC18V512SO20C, the XC18V256SO20C delivers optimal cost-per-bit for Spartan-II/XC2S15-based systems where board space and thermal constraints favor surface-mount SOIC packaging and 256-Kbit capacity suffices for full configuration.

Availability

XC18V256SO20C is available at Aetrix Electronics and suitable for industrial PLCs, avionics reconfigurable modules, and automated test equipment requiring stable component supply, long-lifecycle support, and guaranteed 20-year data retention.

Supply support for XC18V256SO20C 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, specializing in adaptive computing solutions for aerospace, industrial, and communications markets.

The XC18V00 series was designed specifically to provide secure, in-system programmable configuration storage for Xilinx's early-generation FPGAs-including Spartan and Virtex families-enabling field-upgradable, high-integrity boot architectures.

FAQ

What configuration modes does the XC18V256SO20C support?

The XC18V256SO20C supports serial (Master/Slave) and parallel (Slave-Parallel/SelectMAP) configuration modes. Serial mode uses D0 only and operates up to 33 MHz; parallel mode uses D0–D7 and achieves up to 264 Mb/s at 33 MHz. Mode selection is performed via JTAG-programmable control register using Xilinx iMPACT software. The XC18V256SO20C defaults to serial mode after power-up or erase.

How is the CF function implemented on the XC18V256SO20C given its 20-pin SOIC package?

Because the XC18V256SO20C lacks a dedicated CF pin, the CF function is routed to pin 7 (D4) via the CF → D4 programming option. This routing is enabled only when parallel mode is disabled - ensuring D4 remains available as a data pin in parallel configurations. The JTAG CONFIG instruction pulses this pin low for 300–500 ns to initiate FPGA reconfiguration, and it must be connected to the FPGA's PROGRAM pin to function.

What are the power supply requirements for the XC18V256SO20C?

The XC18V256SO20C requires two independent supplies: VCC = +3.3V ±5% for core logic and input buffers, and VCCO = +3.3V or +2.5V for output drivers. All I/O pins are 5V tolerant regardless of supply sequencing order. OE/RESET is an open-drain bidirectional pin pulled high externally (typically 4.7 kΩ to VCC) to release FPGA INIT after power stabilization (~1 ms).

Can multiple XC18V256SO20C devices be cascaded, and how does CEO work?

Yes - XC18V256SO20C devices can be daisy-chained using the CEO (Chip Enable Output) pin. When the internal address counter exceeds the terminal count (TC), CEO goes low and enables the CE input of the next PROM in the chain. CLK and DATA lines are shared across all devices. Cascading allows storage of longer bitstreams or multiple configurations; the XC18V256SO20C's CEO behavior is identical across all XC18V00 family members.

Does the XC18V256SO20C support read protection, and how is it configured?

Yes - the XC18V256SO20C includes a user-settable read security bit that inhibits JTAG readback of the configuration array while permitting program/erase operations. It is configured via Xilinx iMPACT software using the "Security Bit" setting. Once set, the only way to clear it is to perform a full device erase, which resets all memory contents including the security bit itself.