Xilinx FMC Modules: XM500, XM655 & Expansion Cards

Complete guide to Xilinx FMC modules including XM105 debug card, XM500 RFMC balun card, and XM655 breakout card. Covers specifications, compatibility, connector pinouts, and practical setup tips for FPGA and RFSoC evaluation boards.

If you’ve ever tried to evaluate an RFSoC or debug signal integrity on a Virtex-6 board, you know that having the right mezzanine card makes all the difference. I’ve spent countless hours connecting SMA cables to the wrong balun outputs and wondering why my loopback tests showed garbage. This guide covers the essential AMD/Xilinx FMC modules—specifically the Xilinx XM105, Xilinx XM500, and Xilinx XM655—along with practical guidance on selecting the right expansion card for your evaluation setup.

Understanding the FMC Standard

Before diving into specific cards, it’s worth understanding what FMC actually means. The FPGA Mezzanine Card (FMC) standard, defined by ANSI/VITA 57.1, specifies a standardized I/O interface between mezzanine modules and FPGA carrier boards. This standardization means you can use the same daughter card across multiple evaluation platforms, which saves significant development time and cost.

FMC Connector Types: LPC vs HPC

The FMC standard defines two connector configurations that you’ll encounter across all Xilinx evaluation boards:

The critical point here: an LPC mezzanine card will mate with either LPC or HPC carrier connectors. However, HPC cards require HPC connectors on the carrier board. This matters when you’re trying to figure out why your expensive ADC card won’t fit on your SP601.

FMC+ (VITA 57.4) Extension

Newer evaluation boards like the VCK190 and ZCU216 feature FMC+ connectors compliant with VITA 57.4. These extend the transceiver count from 10 to 24 pairs and support data rates up to 28 Gbps. FMC+ maintains backward compatibility—you can plug FMC cards into FMC+ slots, but not vice versa.

Xilinx XM105 Debug Card

The Xilinx XM105 (part number HW-FMC-XM105-G) is one of the most useful tools in any FPGA engineer’s arsenal. It’s essentially a breakout board that provides access to the FMC connector pins through headers and test points.

XM105 Key Features

XM105 Supported Carrier Boards

When to Use the XM105

The XM105 Xilinx debug card excels in these scenarios:

Signal Probing: When you need to verify that your FPGA is actually driving the FMC pins correctly, the XM105’s breakout headers let you attach scope probes or logic analyzers directly to the signals.

Custom Interface Development: If you’re developing a custom FMC card, prototype your interface on the XM105 first. You can wire-wrap connections to the header pins and validate your design before committing to a PCB.

Clock Injection: The SI570 programmable oscillator provides a clean LVDS clock source. Combined with the SMA connectors, you can inject external reference clocks for timing-critical applications.

JTAG Chain Extension: The XM105 includes provisions for extending the JTAG chain through the FMC connector, useful when debugging multi-board configurations.

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XM105 Connector Pinout Reference

The XM105 breaks out signals to multiple connectors:

Xilinx XM500 RFMC Balun Card

The Xilinx XM500 (HW-FMC-XM500) ships with the ZCU111 RFSoC evaluation kit and serves as the primary interface for RF-ADC and RF-DAC signal analysis. Unlike traditional FMC cards, the XM500 uses the RFMC connector standard with dual Samtec LPAM (8×40) connectors.

XM500 Technical Specifications

XM500 Balun Configuration

The XM500 Xilinx card includes multiple balun options to cover different frequency ranges:

XM500 ADC/DAC Channel Mapping

Understanding the channel mapping between the XM500 SMA connectors and the RFSoC banks is critical for successful loopback tests:

XM500 Loopback Test Setup

The typical RF-DAC to RF-ADC loopback test using the XM500 follows this signal path:

1. Test pattern generated on host PC via GUI
2. Pattern sent to ZCU111 via Ethernet
3. Data stored in PL-DDR memory
4. DAC converts digital to analog via XM500 baluns
5. SMA cable connects DAC output to ADC input
6. ADC digitizes received signal
7. Data returned to host for analysis

This workflow validates both the RF data converter performance and the complete signal chain integrity.

Xilinx XM655 Breakout Card

The Xilinx XM655 ships with the ZCU216 and ZCU208 Gen3 RFSoC evaluation kits. While the XM650 provides quick N79 band loopback testing, the XM655 Xilinx breakout card enables in-depth evaluation across the full sub-6GHz frequency range.

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XM655 Frequency Band Configuration

The XM655 Xilinx card organizes channels into three frequency bands:

The frequency ranges and corresponding DAC/ADC connections are silk-screened directly on the XM655 PCB—a helpful reference when you’re wiring up cables at the bench.

XM655 Connector Interface

XM655 Example Design Configuration

For typical RF evaluation using the XM655 and CLK104 clock card:

Evaluation Kit Compatibility Matrix

Selecting the right FMC card for your evaluation board requires matching connector types and supported features:

Third-Party FMC Cards

While Xilinx provides essential debug and RF cards, third-party vendors offer specialized FMC modules for specific applications:

High-Speed Data Converter Cards

Adapter Cards

Practical Design Considerations

Power Budget Planning

FMC cards draw power from the carrier board through the connector. Verify your carrier can supply adequate current:

Signal Integrity Tips

From experience, these issues cause the most headaches:

Cable Length Matching: For high-speed loopback tests, use matched-length SMA cables. A 1ns skew at 2 GHz represents significant phase error.

Balun Selection: The built-in baluns on XM500/XM655 have specific frequency responses. For frequencies outside their optimal range, use the direct SMA connections with external baluns.

DC Blocking: Differential connections on these cards often lack DC blocking capacitors. Add external DC blockers or risk damaging the ADC inputs with DC offset from DAC outputs.

Termination: Verify proper termination at both ends of your signal chain. Unterminated transmission lines cause reflections that look like noise floor degradation.

Useful Resources and Documentation

Official AMD/Xilinx Documentation

Download Links

• AMD Documentation Portal: docs.amd.com
• RFSoC Frequency Planning Tool: Available from AMD website (Excel-based)
• Vivado Design Suite: Required for all Xilinx FPGA development
• RF DC Evaluation Tool: GUI software for RFSoC testing

VITA Standards Resources

• VITA 57.1: FMC base specification
• VITA 57.4: FMC+ specification
• Samtec FMC Connectors: Technical drawings and 3D models
• FMC Hub: Community resource at fmchub.github.io

Frequently Asked Questions

Can I use the XM105 debug card with newer evaluation boards like the ZCU102?

The XM105 uses the VITA 57.1 FMC HPC connector, which is compatible with any board featuring an FMC or FMC+ HPC slot. However, the XM105 was originally designed for Spartan-6 and Virtex-6 boards. While it will physically mate with newer boards, you’ll need to verify the I/O voltage compatibility (VADJ setting) and create your own constraint files since Xilinx doesn’t provide official support for these combinations.

What’s the difference between RFMC and standard FMC connectors?

RFMC (RF Mezzanine Card) uses Samtec LPAM connectors specifically designed for high-frequency RF applications on RFSoC platforms. Standard FMC uses the VITA 57.1 connector designed for general-purpose FPGA I/O. The two are not mechanically compatible—you cannot plug an XM500 into a standard FMC slot or vice versa. RFMC 2.0 used on ZCU216/ZCU208 provides even higher bandwidth for Gen3 RFSoC devices.

Do I need the CLK104 card to use the XM655?

Technically, the ZCU216/ZCU208 can operate without the CLK104 using on-board clocking. However, for serious RF evaluation, the CLK104 is essential. It provides ultra-low-noise reference clocks up to 1.2 GHz internal or 10 GHz external, enabling both PLL-based and direct sampling modes. Without CLK104, you’re limited to the board’s default clock sources, which may not meet your phase noise requirements.

Can third-party FMC cards work with Xilinx evaluation boards?

Yes, any VITA 57.1 compliant FMC card should work with Xilinx FMC-equipped boards, provided connector types match (LPC to LPC/HPC, HPC to HPC only). The challenge is software support—you’ll need to create your own HDL interfaces and device drivers unless the third-party vendor provides Xilinx-specific reference designs. Companies like Analog Devices and HiTech Global often provide Vivado IP and example projects for their FMC products.

How do I determine which SMA connector to use on the XM655 for my target frequency?

The XM655 silk screen indicates frequency bands directly on the PCB, but the general rule is: Low band (10 MHz-1 GHz) uses baluns optimized for lower frequencies, Mid band (1-2 GHz) provides transition coverage, and High band (2-4 GHz) handles higher RF frequencies. For precise frequency planning, use AMD’s RFSoC Frequency Planning Tool spreadsheet to determine optimal sample rates and Nyquist zones, then select the corresponding XM655 channels.

Conclusion

The Xilinx XM105, XM500, and XM655 FMC modules serve distinct but complementary roles in FPGA and RFSoC development. The XM105 remains invaluable for debug and prototyping on traditional FPGA platforms, while the XM500 and XM655 enable comprehensive RF evaluation on RFSoC devices. Understanding the differences between FMC connector types, frequency band coverage, and board compatibility will save you significant time when setting up your evaluation environment. Whether you’re validating a new RF design or debugging signal integrity issues, having the right mezzanine card—and knowing how to use it—makes all the difference.

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Complete guide to Xilinx FMC modules including XM105 debug card, XM500 RFMC balun card, and XM655 breakout card. Covers specifications, compatibility, connector pinouts, and practical setup tips for FPGA and RFSoC evaluation boards.