Xilinx 7 Series Design Guide

Overview

This is in no way meant to replace the comprehensive Xilinx design guides for 7 Series devices, but rather serve as a quick reference guide along with tips and tricks which may not be obvious from reading the official Xilinx material.

IO

The pins in a bank are labelled something like IO_L14P_T2_SRCC_14. What does this mean?

IO This pin can be used as general IO.
L14P This pin is part of a differential pair. The pair number is 14, and this is the positive (P) pin.
T2 The pin is part of bank T2.
   

Decoupling Capacitors

Xilinx gives strict recommendations on the parameters of the capacitors used for decoupling. The following image shows a table with the ESL, ESR and body size limits for the various-valued capacitances.

The parameter value recommendations for decoupling caps used for a Xilinx 7 Series FPGA.
The parameter value recommendations for decoupling caps used for a Xilinx 7 Series FPGA.

Note how there is a range specified for the ESR, it is also bad to have too-little series resistance.

The Kintex and Virtex-7 devices has some in-built decoupling capacitors for the larger package sizes (you still need to add external decoupling caps, just not as many).

Reverse-aspect capacitors can be used for when ultra-low parasitic inductances are required.

Un-used I/O Banks

Using a large device for a small project could mean that there are entire banks of usused I/O pins. In these cases you are allowed to leave the bank’s Vcco pins (e.g. Vcco_14) and I/O pins disconnected. However, for ESD reasons, it is better to connect these pins to either (in order of preference): GND, a valid Vcco voltage, or a floating plane.

MGT’s

The Xiinx 7 Series FPGA’s have in-built Multi-Gigabit Transceivers (MGT’s). These are SerDes capable of 1Gpbs+ transmission rates.

The MGT’s on-board a 7 Series FPGA can be used to implement high-speed communication protocols such as PCIe (PCI Express).

The MGT’s have decision-feedback equalisation (DFE) blocks, which aim to reduce the reduce the inter-symbol interference (ISI) on the current symbol.