AMD XC18V256VQ44I

Overview

XC18V256VQ44I 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 including Spartan-II, Virtex, and Virtex-E families. It supports Master Serial, Slave Serial, Master SelectMAP, and Slave Parallel/SelectMAP modes, features IEEE 1149.1 JTAG boundary-scan, and delivers up to 33 MHz serial clocking or 264 Mb/s parallel throughput. Its VQ44 package enables compact FPGA configuration in industrial-grade temperature range (–40°C to +105°C).

For engineers reviewing the XC18V256VQ44I datasheet, pinout, applications, or equivalent options, key selection criteria include its dual-mode interface flexibility (serial/parallel), JTAG-initiated FPGA reconfiguration via CONFIG instruction, 5V-tolerant I/O compatibility with mixed-voltage systems, 20,000 program/erase cycle endurance, and cascading capability using CEO/CE chaining for multi-FPGA or large-bitstream deployments.

Technical Context

The XC18V256VQ44I 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 IEEE 1149.1 mandatory instructions (BYPASS, SAMPLE/PRELOAD, EXTEST) plus XC18V00-specific CONFIG command that pulses CF low to reset and initiate FPGA configuration.

Configuration mode selection is controlled via a user-accessible register set through JTAG, defaulting to serial mode. Dual output voltage support (3.3V or 2.5V on VCCO) and 5V-tolerant I/O pins enable direct interfacing with legacy 5V logic or modern low-voltage FPGAs without level-shifting circuitry.

Key Specifications

Pinout & Package

XC18V256VQ44I is housed in a 44-pin Very Thin Quad Flat Package (VQFP), RoHS-compliant, with 0.8 mm pitch and 10 mm × 10 mm body size. Pin functions are validated per DS026 (v3.9) Figure 1 and Table 1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with XC18V256PC44I, the XC18V256VQ44I offers superior thermal dissipation and smaller PCB area, while XC18V512VQ44I provides headroom for larger FPGAs without altering layout - making XC18V256VQ44I the balanced choice for cost-sensitive, space-constrained industrial designs.

Availability

XC18V256VQ44I is available at Aetrix Electronics and suitable for industrial control systems, aerospace avionics, and medical imaging equipment requiring stable component supply, long-term lifecycle support, and guaranteed obsolescence management.

Supply support for XC18V256VQ44I 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, delivering high-performance, configurable semiconductor solutions since 1984.

The XC18V00 series was engineered specifically to simplify and harden FPGA configuration in mission-critical systems - emphasizing in-system reprogrammability, JTAG security, and robust mixed-voltage interoperability.

FAQ

What configuration modes does the XC18V256VQ44I support?

The XC18V256VQ44I supports Master Serial, Slave Serial, Master SelectMAP, and Slave Parallel/SelectMAP modes. Mode selection is controlled via a JTAG-accessible user register in the device; serial mode is the default. Each mode defines how the FPGA drives the PROM's CLK and interprets D0 (serial) or D0–D7 (parallel) outputs during configuration - enabling flexible integration across Spartan-II, Virtex, and Virtex-E FPGA families.

How does the JTAG CONFIG instruction work on the XC18V256VQ44I?

The XC18V256VQ44I implements a dedicated JTAG CONFIG instruction (binary 11101110) that pulses the CF pin low for 300–500 ns. When CF is connected to the FPGA's PROGRAM pin, this pulse resets the FPGA and initiates configuration - enabling reconfiguration without power cycling. This function is validated in DS026 and requires no additional hardware, making it ideal for remote or autonomous system updates.

Can the XC18V256VQ44I be used in cascaded configurations?

Yes, the XC18V256VQ44I supports daisy-chain cascading via its CEO (Chip Enable Output) pin, which drives the CE input of the next PROM in the chain. When the internal address counter exceeds terminal count, CEO goes low to enable downstream device output. This allows storage and sequential loading of bitstreams larger than 256 Kbit - confirmed in DS026 Section "Cascading Configuration PROMs" and compatible with other XC18V00 family members.

What is the significance of 5V-tolerant I/Os on the XC18V256VQ44I?

The XC18V256VQ44I features fully 5V-tolerant I/O pins (D0–D7, CLK, CE, OE/RESET, CEO, TCK, TMS, TDI, TDO) despite its 3.3V VCC core supply. This allows direct connection to 5V CMOS logic or legacy FPGA mode pins without level shifters. Power sequencing is also relaxed: VCC may be applied before, after, or simultaneously with 5V signals - a critical advantage in mixed-voltage industrial and test systems.

Does the XC18V256VQ44I support read protection for configuration bitstreams?

Yes, the XC18V256VQ44I includes a user-programmable read security bit that, when set, inhibits JTAG-based reading of the internal bitstream via TDI/TDO. The security bit permits erasure and reprogramming but blocks unauthorized copying - documented in DS026 Table 3 and verified via iMPACT software configuration. This protects intellectual property in deployed systems without compromising field-upgrade capability.