The XC3S400-4PQG208C is a high-performance, cost-optimized field-programmable gate array (FPGA) from Xilinx (now AMD), belonging to the widely adopted Spartan-3 family. Designed for high-volume, cost-sensitive applications, this device combines substantial logic density, flexible I/O, and robust digital signal processing capabilities in a compact 208-pin PQFP package. Whether you are prototyping an embedded controller, building a custom DSP pipeline, or designing a high-speed communication interface, the XC3S400-4PQG208C delivers the programmability and performance engineers demand.
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What Is the XC3S400-4PQG208C?
The XC3S400-4PQG208C is a Spartan-3 series FPGA manufactured by Xilinx. The part number breaks down as follows:
| Part Number Segment |
Meaning |
| XC3S |
Xilinx Spartan-3 Family |
| 400 |
400K System Gates |
| -4 |
Speed Grade (–4, slowest commercial grade) |
| PQ |
Package Type: Plastic Quad Flat Pack (PQFP) |
| G208 |
208-pin package |
| C |
Commercial Temperature Range (0°C to +85°C) |
Key Features and Benefits
The XC3S400-4PQG208C is engineered for applications where logic density, I/O flexibility, and cost efficiency must all be optimized simultaneously. Key highlights include:
- 400,000 system gates equivalent logic capacity
- 8,064 logic cells for implementing complex digital designs
- 56 dedicated 18Kbit block RAMs totaling over 1Mbit of on-chip storage
- 16 dedicated hardware multipliers (18×18 bit) for DSP acceleration
- 4 digital clock managers (DCMs) for clock synthesis, phase shifting, and deskew
- 116 user I/O pins available in the PQ208 package
- Single 1.2V core supply with 3.3V I/O compatibility
- Commercial temperature range (0°C to +85°C)
- Supports multiple I/O standards including LVTTL, LVCMOS, PCI, GTL, SSTL, HSTL, and LVDS
Complete Electrical Specifications
General Device Parameters
| Parameter |
Value |
| Manufacturer |
Xilinx (AMD) |
| Part Number |
XC3S400-4PQG208C |
| Family |
Spartan-3 |
| Technology |
90nm CMOS |
| System Gates |
400,000 |
| Logic Cells |
8,064 |
| CLB Slices |
3,584 |
| Flip-Flops |
7,168 |
| Distributed RAM |
231Kbits |
Memory Resources
| Resource |
Specification |
| Block RAM (18Kbit each) |
56 |
| Total Block RAM |
1,008Kbit (~1Mbit) |
| Distributed RAM |
231Kbits |
DSP and Clocking Resources
| Resource |
Specification |
| Dedicated Multipliers (18×18) |
16 |
| Digital Clock Managers (DCMs) |
4 |
| Max Clock Frequency |
Up to ~326 MHz (internal) |
Package and I/O
| Parameter |
Value |
| Package |
PQFP (Plastic Quad Flat Pack) |
| Pin Count |
208 |
| User I/O Pins |
116 |
| I/O Standards Supported |
LVTTL, LVCMOS 3.3V/2.5V/1.8V/1.5V, PCI 3.3V, SSTL2/SSTL3, HSTL, LVDS, BLVDS |
| Core Supply Voltage (VCCINT) |
1.2V |
| I/O Supply Voltage (VCCO) |
1.2V – 3.3V |
Operating Conditions
| Parameter |
Value |
| Temperature Range |
0°C to +85°C (Commercial) |
| VCCINT (Core) |
1.14V – 1.26V |
| VCCO (I/O) |
1.14V – 3.6V (bank dependent) |
Package Dimensions and Footprint
The PQ208 package (PQFP, 208-pin) is a standard plastic quad flat pack with a fine-pitch lead arrangement. Key mechanical data:
| Dimension |
Value |
| Package Type |
PQFP (Plastic Quad Flat Pack) |
| Total Pins |
208 |
| Body Size |
28mm × 28mm (nominal) |
| Lead Pitch |
0.50mm |
| Mounting Type |
Surface Mount (SMD) |
| Height (max) |
3.4mm |
Functional Block Overview
The XC3S400 architecture is built around four core resource types that work together to implement virtually any digital design:
#### 1. Configurable Logic Blocks (CLBs)
Each CLB contains two slices, and each slice has two 4-input look-up tables (LUTs), two flip-flops, and carry/arithmetic logic. With 3,584 slices total, the XC3S400 can implement complex state machines, control logic, and arithmetic pipelines.
#### 2. Block RAM (BRAM)
The 56 on-chip 18Kbit block RAMs are true dual-port memories supporting independent clocking on each port. They can be configured as standard RAMs, FIFOs, or ROM structures, making them ideal for data buffering, lookup tables, and embedded microcontroller memory.
#### 3. Dedicated Multipliers
The 16 hardware 18×18-bit multipliers provide full-speed multiply operations without consuming CLB resources. They are optimized for DSP operations such as FIR filters, FFT butterflies, and PID controllers.
#### 4. Digital Clock Managers (DCMs)
The four DCMs support clock frequency synthesis (using DLL and DCM), phase shifting (0°–360° in fine steps), and clock deskewing. This makes the XC3S400 ideal for designs requiring precise clock domain management or reference clock generation.
Supported I/O Standards
The XC3S400-4PQG208C supports a rich set of single-ended and differential I/O standards:
| I/O Standard |
Description |
| LVTTL |
Low-voltage TTL (3.3V) |
| LVCMOS 3.3V / 2.5V / 1.8V / 1.5V |
Low-voltage CMOS at multiple supply levels |
| PCI 3.3V |
PCI bus compliance at 3.3V |
| SSTL2 / SSTL3 |
Stub Series Terminated Logic for SDRAM/DDR interfaces |
| HSTL |
High-Speed Transceiver Logic |
| GTL / GTL+ |
Gunning Transceiver Logic |
| LVDS |
Low Voltage Differential Signaling |
| BLVDS |
Bus LVDS for multi-drop differential buses |
Ordering Information
| Parameter |
Detail |
| Manufacturer Part Number |
XC3S400-4PQG208C |
| Manufacturer |
Xilinx (AMD) |
| Status |
Active / Legacy (check distributor for stock) |
| Package |
208-PQFP |
| Operating Temperature |
0°C ~ 85°C |
| Moisture Sensitivity Level |
MSL 3 |
| RoHS Compliance |
RoHS Compliant versions available (check suffix) |
Typical Applications
The XC3S400-4PQG208C is a versatile FPGA used across a broad range of industries and application domains:
| Application Domain |
Typical Use Case |
| Industrial Automation |
Motor control, PLC replacement, sensor fusion |
| Communications |
UART, SPI, I²C, Ethernet MAC, protocol bridging |
| Consumer Electronics |
Video processing, display timing controllers |
| Automotive |
LIDAR preprocessing, CAN/LIN interface logic |
| Medical Devices |
Signal acquisition, real-time filtering |
| Test & Measurement |
Pattern generation, logic analyzers |
| Education & Prototyping |
FPGA learning platforms, soft-core processors |
XC3S400 vs. Other Spartan-3 Devices
| Device |
System Gates |
Logic Cells |
Block RAMs |
Multipliers |
I/O (max) |
| XC3S50 |
50K |
1,728 |
4 |
4 |
124 |
| XC3S200 |
200K |
4,320 |
12 |
12 |
173 |
| XC3S400 |
400K |
8,064 |
56 |
16 |
264 |
| XC3S1000 |
1M |
17,280 |
24 |
24 |
391 |
| XC3S1500 |
1.5M |
29,952 |
32 |
32 |
487 |
The XC3S400 represents an optimal mid-range choice: substantially more capable than entry-level Spartan-3 devices, yet significantly more affordable than higher-density parts.
Design Tool Support
The XC3S400-4PQG208C is fully supported by Xilinx ISE Design Suite (ISE 14.7 is the final version supporting Spartan-3). Key tools include:
- ISE Project Navigator – RTL entry, synthesis, and implementation
- XST (Xilinx Synthesis Technology) – HDL synthesis engine
- PlanAhead – Floorplanning and timing closure
- iMPACT – JTAG-based device programming
- ChipScope Pro – On-chip logic analysis
Third-party support is also available from tools including Mentor Precision, Synplify Pro, and ModelSim/Questa for simulation.
Configuration and Programming
The XC3S400 can be configured using several standard methods:
| Configuration Mode |
Description |
| Master Serial (SPI Flash) |
Autonomous boot from an external SPI Flash |
| Master SelectMAP |
Byte-wide parallel configuration bus |
| Slave Serial |
Controlled by external host via serial bitstream |
| Slave SelectMAP |
Host-controlled parallel configuration |
| JTAG |
Boundary-scan and direct configuration via JTAG port |
The device uses an external bitstream stored in SPI Flash (e.g., Xilinx Platform Flash XCF series) or a parallel NOR Flash for production deployments.
Frequently Asked Questions (FAQ)
Q: What is the difference between XC3S400-4PQG208C and XC3S400-4PQG208I? The suffix “C” denotes the Commercial temperature range (0°C to +85°C), while “I” denotes the Industrial temperature range (–40°C to +100°C). All other specifications are identical.
Q: Is the XC3S400-4PQG208C RoHS compliant? Lead-free RoHS compliant versions are available. Verify the exact suffix and packaging marking when ordering from your distributor to confirm compliance.
Q: Can I replace a Spartan-3 with a Spartan-6 or 7-series FPGA? Spartan-6 and 7-series devices are not pin-compatible with Spartan-3 and use different toolchains (ISE vs. Vivado). A design migration requires re-targeting the pinout and re-synthesizing the HDL, but the IP is portable.
Q: What soft-core processors are supported? The XC3S400 has sufficient resources to implement Xilinx MicroBlaze (32-bit RISC) or PicoBlaze (8-bit) soft processors directly in the FPGA fabric.
Summary
The XC3S400-4PQG208C remains a proven, reliable choice for embedded logic design, digital signal processing, and interface bridging applications. Its 400K gate capacity, 16 hardware multipliers, 1Mbit of block RAM, and support for a wide variety of I/O standards make it a flexible platform for both legacy system maintenance and new design prototyping. Its commercial-grade temperature rating and compact 208-pin PQFP footprint make it straightforward to integrate into cost-sensitive production designs.
Engineers looking to maximize value while retaining access to a mature, well-documented FPGA ecosystem will find the XC3S400-4PQG208C an enduringly capable solution.
