Gigabit Transceivers
Access to 28 high-speed serial transceiver pairs (28 Rx and 28 Tx) corresponding to 5 GTH quads (224, 225, 226, 227 and 228) and 2 GTY quads (129 and 130) on the FPGA are available on the expansion connectors. The MGTREFCLK 0 for every transceiver quad is also routed to the associated expansion connector. For full connection details see the XEM8370 Pin List.
| MGT Quad | FPGA Supported Bitrate (-1 speed) |
|---|---|
| GTY 129 | 16.3 Gbps |
| GTY 130 | 16.3 Gbps |
| GTH 224 | 12.5 Gbps |
| GTH 225 | 12.5 Gbps |
| GTH 226 | 12.5 Gbps |
| GTH 227 | 12.5 Gbps |
| GTH 228 | 12.5 Gbps |
AC-Coupling
0.01μF AC-coupling capacitors are installed between the expansion connectors and the FPGA for all MGTREFCLK signals.
AC-coupling capacitors are not installed for any of the transceiver transmit or receive pairs. If AC-coupling is desired or required for the serial application, they should be installed on the peripheral side (your board).
IBERT Configuration
AMD provides the IBERT tool to test and experiment with gigabit transceivers. Appropriate MGTREFCLK’s must be supplied to the GTY and GTH banks through the expansion connectors. The settings below are compatible with the XEM8370 using Vivado 2022.2:
| PROTOCOL DEFINITION | ||
|---|---|---|
| Protocol | Custom 1 | |
| Line Rate | GTY: 16.3 Gbps GTH: 12.5 Gbps | |
| Data Width | 40 | |
| Ref Clk | 100.000 MHz | |
| Quad Count | 7 | |
| PLL | QPLL0 | |
| PROTOCOL SELECTION | ||
| GTX Location | Protocol Selected | Refclk Selection |
| QUAD_129 | Custom 1 / 16.3Gbps | MGTREFCLK0_129 |
| QUAD_130 | Custom 1 / 16.3Gbps | MGTREFCLK0_129 |
| QUAD_224 | Custom 1 / 12.5Gbps | MGTREFCLK0_226 |
| QUAD_225 | Custom 1 / 12.5Gbps | MGTREFCLK0_226 |
| QUAD_226 | Custom 1 / 12.5Gbps | MGTREFCLK0_226 |
| QUAD_227 | Custom 1 / 12.5Gbps | MGTREFCLK0_226 |
| QUAD_228 | Custom 1 / 12.5Gbps | MGTREFCLK0_226 |
| CLOCK SETTINGS | ||
| Add RXOUTCLK Probes | Unchecked | |
| Clock Type | System Clock | |
| Source | External | |
| I/O Standard | LVDS | |
| P Package Pin | E22 | |
| Frequency | 100 MHz | |
| Enable DIFF Term. | Unchecked |
Gigabit Transceiver IBERT Performance
AMD’s IBERT tool enables an automated self-measurement of a GTH channel’s eye diagram when used in a loopback mode. Eye diagrams for two different speeds were captured using this tool with a simple loopback peripheral attached to the expansion headers. While results may vary, these are typical captures and actually represent the worst case capture over all channels for the respective rates.
Note that in loopback modes, it can be helpful to disable the GBT DFE (decision feedback equalizer) to avoid over-compensation. The TX Diff Swing must also be set so that it does not over saturate the receiver.
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