The XC3S400-4FG320C is a mid-range, commercially graded Xilinx FPGA from AMD’s Spartan-3 family, housed in a 320-ball Fine-pitch Ball Grid Array (FBGA) package. With 400,000 system gates, a -4 speed grade, and robust I/O flexibility, this device is a proven choice for cost-sensitive embedded systems, digital signal processing, and communication applications. This guide covers every specification, feature, and application consideration you need to make a confident purchasing decision.
What Is the XC3S400-4FG320C?
The XC3S400-4FG320C is a field-programmable gate array (FPGA) manufactured by AMD (formerly Xilinx). It belongs to the Spartan-3 generation — a family designed to deliver high logic density at low cost. The “4” in the part number designates the speed grade, “FG320” indicates the 320-ball FBGA package, and “C” denotes the commercial temperature range (0°C to +85°C).
This device is widely used in production hardware, prototyping platforms, and legacy designs that require a reliable, well-supported programmable logic solution.
XC3S400-4FG320C Key Specifications
| Parameter |
Value |
| Manufacturer |
AMD (Xilinx) |
| Part Number |
XC3S400-4FG320C |
| Series |
Spartan-3 |
| Logic Cells |
8,064 |
| System Gates |
400,000 |
| CLB Flip-Flops |
7,168 |
| Distributed RAM |
56 Kb |
| Block RAM |
288 Kb |
| Multipliers (18×18) |
16 |
| DCMs (Digital Clock Managers) |
4 |
| I/O Standards Supported |
26 |
| Maximum User I/O Pins |
264 |
| Package |
FG320 (FBGA, 320-Ball) |
| Package Dimensions |
15 mm × 15 mm |
| Speed Grade |
-4 |
| Operating Voltage (VCCINT) |
1.2 V |
| Temperature Range |
0°C to +85°C (Commercial) |
| RoHS Status |
RoHS Compliant |
XC3S400-4FG320C Package and Pinout Overview
FG320 FBGA Package Details
| Package Attribute |
Detail |
| Package Type |
Fine-Pitch Ball Grid Array (FBGA) |
| Ball Count |
320 |
| Body Size |
15 mm × 15 mm |
| Ball Pitch |
1.0 mm |
| Mounting Type |
Surface Mount Technology (SMT) |
| Max User I/Os |
264 |
The compact 15 × 15 mm footprint of the FG320 package makes the XC3S400-4FG320C ideal for board designs with tight spatial constraints. Its 1.0 mm ball pitch is compatible with standard PCB fabrication processes, keeping manufacturing costs low.
Logic Architecture and On-Chip Resources
Configurable Logic Blocks (CLBs)
The Spartan-3 CLB architecture is organized into a matrix of slices, each containing:
- Look-Up Tables (LUTs) for implementing combinatorial logic
- Storage elements (flip-flops and latches)
- Wide multiplexers for routing and function generation
- Carry and arithmetic logic chains for efficient adder/subtractor implementation
Memory Resources
| Memory Type |
Capacity |
| Distributed RAM |
56 Kb |
| Block RAM (BRAM) |
288 Kb (16 × 18 Kb blocks) |
Block RAM in the XC3S400 supports true dual-port operation, making it suitable for FIFOs, lookup tables, and frame buffers in embedded video or communication applications.
DSP and Arithmetic Resources
The device integrates 16 dedicated 18×18-bit hardware multipliers, enabling efficient implementation of multiply-accumulate (MAC) operations without consuming CLB resources. This is particularly valuable in DSP, filtering, and motor control applications.
Clock Management
| DCM Feature |
Detail |
| Number of DCMs |
4 |
| Functions |
Clock multiplication, division, phase shifting, deskewing |
| DLL Frequency Range |
24 MHz to 326 MHz |
The four Digital Clock Managers (DCMs) provide flexible clock synthesis and management, supporting designs that require multiple clock domains or precise phase relationships.
I/O Features and Supported Standards
I/O Bank Organization
The XC3S400-4FG320C organizes its I/O pins into multiple banks, each independently configurable for voltage and I/O standard. This allows a single device to interface with multiple voltage domains on the same board.
Supported I/O Standards
| Category |
Supported Standards |
| Single-Ended |
LVTTL, LVCMOS 3.3V / 2.5V / 1.8V / 1.5V / 1.2V |
| Differential |
LVDS, LVDS_25, BLVDS, LVPECL, RSDS |
| Legacy / PCI |
PCI 3.3V, PCI-X |
| High-Speed |
HSTL Class I/II, SSTL2 Class I/II, SSTL3 Class I/II |
With support for 26 I/O standards, the XC3S400-4FG320C is highly adaptable to mixed-voltage board environments.
Electrical Characteristics
Absolute Maximum Ratings
| Parameter |
Min |
Max |
| VCCINT (Core Voltage) |
–0.5 V |
1.32 V |
| VCCO (I/O Voltage) |
–0.5 V |
4.0 V |
| Storage Temperature |
–65°C |
+150°C |
| Operating Temperature (Commercial) |
0°C |
+85°C |
Typical Power Consumption
Power consumption depends heavily on design activity, clock frequency, and I/O loading. Xilinx provides the XPower Estimator tool for accurate pre-layout power analysis.
| Supply Rail |
Nominal Voltage |
| VCCINT |
1.20 V |
| VCCO |
1.2 V – 3.3 V (I/O bank dependent) |
| VCCAUX |
2.5 V |
Configuration Modes
The XC3S400-4FG320C supports multiple configuration modes, providing flexibility for different system architectures:
| Configuration Mode |
Description |
| Master Serial |
Uses an external serial Flash (e.g., Xilinx Platform Flash) |
| Slave Serial |
Driven by an external microprocessor or FPGA |
| Master SPI |
Interfaces directly with standard SPI Flash memory |
| Master BPI |
Parallel NOR Flash configuration |
| JTAG |
In-system programming and debug via IEEE 1149.1 boundary scan |
| Slave SelectMAP |
Byte-wide parallel configuration by a host processor |
The JTAG interface is invaluable for in-circuit debugging and iterative firmware development without removing the device from the board.
Speed Grade -4 Performance
The “-4” speed grade is the fastest commercially available speed grade for the Spartan-3 family. It supports higher clock frequencies and shorter propagation delays compared to -5 or -4C grades in other contexts. Key timing parameters:
| Timing Parameter |
Value (Typical, -4 Grade) |
| Maximum Flip-Flop Frequency |
Up to ~326 MHz (DCM output) |
| CLB Logic Propagation Delay |
Sub-nanosecond (LUT path) |
| I/O Setup Time |
See Spartan-3 DC & Switching Characteristics datasheet |
For timing-critical designs, Xilinx ISE or Vivado (legacy) static timing analysis tools should be used alongside the device-specific timing models provided in the official datasheet.
Comparison: XC3S400-4FG320C vs. Related Spartan-3 Variants
| Part Number |
Gates |
Block RAM |
Multipliers |
Package |
Speed Grade |
Temp |
| XC3S400-4FG320C |
400K |
288 Kb |
16 |
FG320 |
-4 |
Commercial |
| XC3S400-4PQ208C |
400K |
288 Kb |
16 |
PQ208 |
-4 |
Commercial |
| XC3S400-4FG320I |
400K |
288 Kb |
16 |
FG320 |
-4 |
Industrial |
| XC3S200-4FG256C |
200K |
216 Kb |
12 |
FG256 |
-4 |
Commercial |
| XC3S1000-4FG320C |
1M |
432 Kb |
24 |
FG320 |
-4 |
Commercial |
| XC3S1500-4FG320C |
1.5M |
576 Kb |
32 |
FG320 |
-4 |
Commercial |
The XC3S400-4FG320C occupies the mid-range sweet spot of the Spartan-3 family — offering substantially more resources than the XC3S200 while sharing the same compact FG320 footprint as higher-density variants, enabling easy design scalability.
Typical Application Areas
Embedded System Control
The combination of 8,064 logic cells, block RAM, and hardware multipliers makes the XC3S400-4FG320C a capable controller for embedded peripherals, custom CPU implementations (e.g., MicroBlaze soft processor), and custom state machines.
Digital Signal Processing (DSP)
With 16 dedicated hardware multipliers and efficient CLB arithmetic chains, the device is well-suited for FIR/IIR filters, FFT engines, and digital modulation/demodulation in communications systems.
Communications and Networking
Support for LVDS, SSTL, HSTL, and other high-speed I/O standards enables the XC3S400-4FG320C to interface with high-speed memory, serial transceivers, and line-rate logic in Ethernet, SPI, I2C, UART, and custom protocol implementations.
Industrial Automation
The commercial temperature range (0°C to +85°C) covers the majority of industrial control environments. The device is commonly found in motor drive controllers, sensor interfaces, and real-time control loops.
Video and Imaging
Block RAM depth and distributed memory support line-buffer and frame-buffer implementations for VGA, CameraLink, or custom video pipeline designs.
Development Tools and Design Flow
Xilinx ISE Design Suite
The XC3S400-4FG320C is supported by Xilinx ISE Design Suite (the legacy toolchain), which provides:
- HDL synthesis (VHDL/Verilog)
- Placement and routing
- Static timing analysis
- Bitstream generation and configuration
ISE 14.7 is the final version and remains freely downloadable from the AMD/Xilinx website.
CORE Generator and IP Cores
ISE includes CORE Generator, which offers pre-verified IP cores including:
- FIFO generators
- Block memory controllers
- DCM/PLL wrappers
- Communication interfaces (UART, SPI, I2C)
- DSP building blocks
ChipScope Pro
Xilinx’s ChipScope Pro embeds logic analyzer functionality directly into the FPGA fabric, enabling in-system signal capture without external test equipment — essential for debugging complex timing issues.
Ordering and Availability
| Attribute |
Detail |
| Part Number |
XC3S400-4FG320C |
| Manufacturer |
AMD (Xilinx) |
| Manufacturer Series |
Spartan-3 |
| Package |
FG320 (FBGA 320-Ball) |
| Operating Temperature |
0°C ~ 85°C |
| Moisture Sensitivity Level |
MSL 3 |
| RoHS |
Compliant |
| ECCN |
3A991.a.2 |
| HTSUS |
8542.39.00.01 |
Frequently Asked Questions (FAQ)
Q: What is the difference between XC3S400-4FG320C and XC3S400-4FG320I? The only difference is the temperature rating. The “C” suffix designates a commercial range (0°C to +85°C), while the “I” suffix designates an industrial range (–40°C to +100°C). All logic and electrical characteristics are otherwise identical.
Q: Is the XC3S400-4FG320C still in production? The Spartan-3 family is in the mature/end-of-life phase. It is still available through authorized distributors and component brokers, but designers starting new projects should evaluate Spartan-6, Artix-7, or newer Xilinx families for long-term availability.
Q: What programming software do I need? Use Xilinx ISE Design Suite 14.7 for synthesis, implementation, and bitstream generation. This is the last version to officially support the Spartan-3 family and is available free of charge.
Q: Can I use a JTAG programmer to configure the XC3S400-4FG320C? Yes. The device supports IEEE 1149.1 JTAG configuration and boundary scan. Compatible programmers include the Xilinx Platform Cable USB II and compatible third-party JTAG tools.
Q: What voltage does the XC3S400-4FG320C core require? The core (VCCINT) requires 1.2 V. I/O banks (VCCO) can range from 1.2 V to 3.3 V depending on the I/O standard in use. An auxiliary supply (VCCAUX) of 2.5 V is also required.
Summary
The XC3S400-4FG320C is a well-documented, cost-effective FPGA that delivers 400K system gates, 288 Kb of block RAM, 16 hardware multipliers, and 4 DCMs in a compact 15 × 15 mm BGA package. Its broad I/O standard support and -4 speed grade make it a versatile choice for embedded control, DSP, and communications applications. While the Spartan-3 family is mature, the XC3S400-4FG320C remains a dependable solution for both legacy system maintenance and new designs where proven silicon and comprehensive documentation are priorities.
