Digilent 410-274P-KIT - Manual (Page 9)

Nexys4™ FPGA Board Reference Manual
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Page 9 of 29
clocking resources that can be inserted into the user’s design. The clocking wizard can be accessed from within the
Project Navigator or Core Generator tools.
6 USB-UART Bridge (Serial Port)
The Nexys4 includes an FTDI FT2232HQ USB-UART bridge (attached to connector J6) that allows you use PC
applications to communicate with the board using standard Windows COM port commands. Free USB-COM port
drivers, available from www.ftdichip.com under the "Virtual Com Port" or VCP heading, convert USB packets to
UART/serial port data. Serial port data is exchanged with the FPGA using a two-wire serial port (TXD/RXD) and
optional hardware flow control (RTS/CTS). After the drivers are installed, I/O commands can be used from the PC
directed to the COM port to produce serial data traffic on the C4 and D4 FPGA pins.
Two on-board status LEDs provide visual feedback on traffic flowing through the port: the transmit LED (LD20) and
the receive LED (LD19). Signal names that imply direction are from the point-of-view of the DTE (Data Terminal
Equipment), in this case the PC.
The FT2232HQ is also used as the controller for the Digilent USB-JTAG circuitry, but the USB-UART and USB-JTAG
functions behave entirely independent of one another. Programmers interested in using the UART functionality of
the FT2232 within their design do not need to worry about the JTAG circuitry interfering with the UART data
transfers, and vice-versa. The combination of these two features into a single device allows the Nexys4 to be
programmed, communicated with via UART, and powered from a computer attached with a single Micro USB
cable.
The connections between the FT2232HQ and the Artix-7 are shown in Figure 6.
TXD C4
Micro-USB
(J6)
2
RXD
Artix-7 FT2232
CTS
RTS
JTAG
4
JTAG
D4
D3
E5
7 USB HID Host
The Auxiliary Function microcontroller (Microchip PIC24FJ128) provides the Nexys4 with USB HID host capability.
After power-up, the microcontroller is in configuration mode, either downloading a bitstream to the FPGA, or
waiting to be programmed from other sources. Once the FPGA is programmed, the microcontroller switches to
application mode, which is USB HID Host in this case. Firmware in the microcontroller can drive a mouse or a
keyboard attached to the type A USB connector at J5 labeled "USB Host.” Hub support is not currently available, so
only a single mouse or a single keyboard can be used. The PIC24 drives several signals into the FPGA – two are
used to implement a standard PS/2 interface for communication with a mouse or keyboard, and the others are
connected to the FPGA’s two-wire serial programming port, so the FPGA can be programmed from a file stored on
a USB pen drive or microSD card.
Figure 6. Nexys4 FT2232HQ connections