XC6SLX45 & XC6SLX45T: High-Capacity Spartan-6 Guide

When a project outgrows the mid-range Spartan-6 devices but doesn’t warrant the cost of the XC6SLX75 or larger, the XC6SLX45 and XC6SLX45T hit the sweet spot. With 43,661 logic cells, 58 DSP slices, and over 2 Mb of block RAM, these devices handle serious workloads—video processing, multi-channel signal processing, and complex embedded systems. I’ve used the XC6SLX45 on several video processing boards where it comfortably handled 1080p pipelines that would have choked smaller devices.

This guide covers both variants in detail: the logic-optimized XC6SLX45 (LX series) and the transceiver-equipped XC6SLX45T (LXT series), helping you determine which fits your application and how to get the most from these high-capacity Spartan-6 FPGAs.

Understanding the XC6SLX45 vs XC6SLX45T Difference

The fundamental distinction between these two devices comes down to high-speed serial transceivers. Both share identical logic resources, but the XC6SLX45T adds GTP transceivers and a hard PCIe endpoint block—features that justify the “T” suffix and higher price point.

XC6SLX45 vs XC6SLX45T Comparison

Choose the XC6SLX45 when your design needs maximum I/O count and doesn’t require high-speed serial interfaces. Select the XC6SLX45T when you need PCIe connectivity, SATA, Aurora, or other protocols requiring the GTP transceivers.

XC6SLX45 Complete Specifications

Core Logic Resources

The XC6SLX45 provides nearly triple the logic capacity of the XC6SLX16, making it suitable for complex state machines, multi-protocol interfaces, and designs requiring significant parallel processing.

Block RAM Configuration

The substantial block RAM capacity enables frame buffering for video applications, large lookup tables, and multi-channel audio processing without external memory.

DSP48A1 Slice Details

With 58 DSP slices, the XC6SLX45 supports complex signal processing applications including multi-channel FIR filters, FFT implementations, and image processing algorithms requiring substantial multiply-accumulate throughput.

Clock Management Resources

The four CMTs provide extensive clocking flexibility for multi-clock-domain designs common in video processing and communication applications.

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XC6SLX45T GTP Transceiver Specifications

The XC6SLX45T includes four GTP (Gigabit Transceiver) tiles, enabling high-speed serial communication without external PHY devices.

GTP Transceiver Features

Supported High-Speed Protocols

The integrated PCIe endpoint block in the XC6SLX45T eliminates the need for soft PCIe IP, saving significant logic resources and simplifying timing closure.

Package Options for XC6SLX45 and XC6SLX45T

XC6SLX45 Available Packages

XC6SLX45T Available Packages

Note that the XC6SLX45T in CSG324 package only provides 2 GTP transceivers—the smaller package cannot route all four. For full transceiver access, use CSG484 or larger.

Speed Grades and Power Considerations

Available Speed Grades

The -3 speed grade achieves maximum performance with internal logic exceeding 500 MHz for simple paths. The -1L option reduces core voltage to 1.0V for power-sensitive applications but is not available for the XC6SLX45T.

Power Supply Requirements

The XC6SLX45T requires additional power rails (MGTAVCC, MGTAVTT) for the GTP transceivers—plan your power distribution accordingly.

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Memory Controller Block (MCB) Features

Both the XC6SLX45 and XC6SLX45T include two hard Memory Controller Blocks, enabling high-performance DDR3/DDR2/DDR/LPDDR interfaces without consuming logic resources.

MCB Specifications

Each MCB supports independent memory devices, enabling configurations like dual 256 MB DDR3 banks or a single wider interface with interleaving.

Practical Applications for XC6SLX45 and XC6SLX45T

Video Processing Applications

The XC6SLX45 excels in video processing thanks to its substantial block RAM and DSP resources:

Research implementations have demonstrated real-time digital image stabilization on the XC6SLX45 achieving 104 frames per second for 480p video with only 24 mW power consumption in the FPGA fabric.

Communication and Networking

Industrial Control Systems

Development Boards Featuring XC6SLX45 and XC6SLX45T

Several development platforms support prototyping with these devices:

The Digilent Atlys was particularly popular for academic video processing projects, offering HDMI input/output alongside the XC6SLX45 FPGA.

Configuration and Programming

Configuration File Sizes

Recommended Configuration Flash

Configuration time from SPI flash at 33 MHz CCLK takes approximately 350 ms for the XC6SLX45—acceptable for most applications but consider BPI mode for faster startup requirements.

Design Considerations and Best Practices

Power Distribution

The XC6SLX45 and XC6SLX45T require careful power sequencing:

1. VCCINT must ramp before or with VCCAUX
2. VCCO banks can power independently
3. For LXT devices, MGTAVCC and MGTAVTT require dedicated regulators
4. Use bulk and bypass capacitors per Xilinx recommendations (UG393)

PCB Layout Guidelines

Useful Resources and Documentation

Official AMD/Xilinx Documentation

Software and IP Downloads

• ISE Design Suite 14.7 WebPACK — Free download from AMD/Xilinx
• ISE Windows 10/11 VM — Pre-configured virtual machine
• LogiCORE PCIe Endpoint — For XC6SLX45T designs
• MIG (Memory Interface Generator) — DDR3/DDR2 controller generation

Development Board Resources

• Digilent Atlys — Schematics, reference designs (archived)
• Numato Galatea — Documentation, PCIe examples
• ALINX AX545 — Tutorials, Verilog demos

Frequently Asked Questions

What’s the main advantage of XC6SLX45T over XC6SLX45?

The XC6SLX45T includes four GTP transceivers capable of 3.2 Gb/s and a hard PCIe Gen1 endpoint block. If your design requires PCIe, SATA, DisplayPort, or other high-speed serial protocols, the LXT variant eliminates the need for external PHY devices and saves substantial logic resources. The standard XC6SLX45 offers more user I/O pins (358 vs 296) and lower cost when transceivers aren’t needed.

Can I use Vivado with the XC6SLX45 or XC6SLX45T?

No, Vivado does not support any Spartan-6 devices. You must use ISE Design Suite 14.7, available free as WebPACK edition. ISE runs on Windows 7 natively or via AMD’s provided virtual machine image on Windows 10/11. While ISE lacks modern features like incremental compilation, it remains stable and well-documented for Spartan-6 development.

How does the XC6SLX45 compare to Spartan-7 devices?

The XC6SLX45 offers more logic cells than the XC7S50 (43,661 vs 52,160) but uses older 45nm technology versus Spartan-7’s 28nm. Key differences include Spartan-6’s hard memory controller (absent in Spartan-7), different block RAM architecture (18Kb vs 36Kb granularity), and ISE versus Vivado tool support. Spartan-6 typically costs less for equivalent logic but consumes more power.

What applications are best suited for the XC6SLX45?

The XC6SLX45 excels in video processing (frame buffers, image processing, scaling), industrial control (multi-axis motor control, PLC coprocessing), communication systems (protocol bridging, Ethernet MAC), and embedded systems requiring substantial logic with DDR3 memory interface. The 58 DSP slices and 2 Mb block RAM enable demanding signal processing applications.

Is the XC6SLX45 still in production and available?

Yes, both the XC6SLX45 and XC6SLX45T remain in production under AMD’s extended Spartan-6 lifecycle through at least 2030. However, lead times can be extended due to fab constraints on mature process nodes. For new designs, verify current availability with distributors and consider long-term supply when planning production volumes.

Conclusion

The XC6SLX45 and XC6SLX45T represent the high-capacity sweet spot in the Spartan-6 family—substantial logic resources, generous block RAM, and powerful DSP capabilities at a price point below the XC6SLX75 tier. The LX variant serves pure logic applications with maximum I/O count, while the LXT variant adds GTP transceivers and PCIe for high-speed serial connectivity.

For video processing, industrial control, and embedded systems requiring more than mid-range devices can offer, these FPGAs deliver proven performance backed by mature tools and extensive documentation. The hard memory controller blocks simplify DDR3 integration, and the four clock management tiles support complex multi-domain designs.

Whether you’re maintaining existing products, developing new embedded systems, or prototyping high-speed interfaces, the XC6SLX45 and XC6SLX45T provide capable, cost-effective platforms that continue to serve the FPGA community well into the current decade.