Digilent NetFPGA-SUME Справочное руководство - Страница 18

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NetFPGA-SUME™ Reference Manual

3.3V VCC signals (pins 6 and 12), two Ground signals (pins 5 and 11), and eight logic signals, as shown below. The

VCC and Ground pins can deliver up to 1A of current. Pmod data signals are not matched pairs, and they are

routed using best-available tracks without impedance control or delay matching.

The signals on the Pmod port are connected to the FPGA via two 4-bit dual-supply bus transceivers (IC1 and IC2,

part number SN74AVC4T774) with configurable voltage translation and 3-state outputs. You need to specifically

set DIR for each pin to control the signal direction. The bus transceiver is enabled by driving OE pin of the bus

transceiver low.

Basic I/O

The NetFPGA-SUME board includes two LEDs (LD0 and LD1) and two pushbuttons (BTN0 and BTN1) that can be

used for basic user I/O. These can be useful for debugging designs. The pushbuttons are connected to the FPGA via

series resistors to prevent damage from inadvertent short circuits (a short circuit could occur if an FPGA pin

assigned to a pushbutton or slide switch was inadvertently defined as an output). The two pushbuttons are

"momentary" switches that normally generate a low output when they are at rest, and a high output only when

they are pressed.

The two LEDs are green and are illuminated when driven high. It is possible to control the brightness by providing a

pulse-width modulated signal that varies the duty cycle from 0% to 100%.

An additional red pushbutton (BTN3, labeled PROG) is attached to the PROGRAM_B pin of the Virtex-7 FPGA.

Pressing this button will clear the configuration inside the FPGA and cause the DONE pin to go low. If the mode

jumper is not shorted, this will also trigger the CPLD to reprogram the FPGA with a bitstream stored in flash (See

the

"FPGA

Configuration" section for more info).

LD4 is attached to the DONE pin of the FPGA, and is illuminated whenever the FPGA is configured with a valid

bitstream.

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