Data Sheet

Nexys Video™ FPGA Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
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Page 15 of 29
7.2 Serial Peripheral Interface (DSPI)
An industry-standard SPI interface can also be used for transferring data. It uses only four signals for serial full-
duplex communication. The USB controller acts as a SPI master, with the FPGA taking the slave role. The USB
controller initiates a transaction after API function calls are made and transfers data in both directions
simultaneously.
Signal
Direction (FPGA)
Description
SCK
Input
Data bus.
MOSI
Output
When low, data is available for reading from the FIFO.
MISO
Input
When low, data can be written to the FIFO.
SS
Input
A low-pulse triggers data to be read out from the FIFO.
Table 6. DSPI signal description.
For more information, see the FT2232H data sheet.
8 USB HID Host
The Auxiliary Function microcontroller (Microchip® PIC24FJ128) provides the Nexys Video with USB HID host
capability. After power-up, the microcontroller is in configuration mode, either downloading a bitstream to the
FPGA or waiting on it 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 J15 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.
Artix-7
W17
PIC24FJ128
PS2_CLK
N13
HOST (J15)
2
PS2_DAT
FPGA
Config
microSD
2
FPGA
Config
User I/O
SD MICRO (J3)
SD/USB (JP3)
Figure 7. Nexys Video PIC24 connections.
8.1 HID Controller
The Auxiliary Function microcontroller hides the USB HID protocol from the FPGA and emulates an old-style PS/2
bus. The microcontroller behaves just like a PS/2 keyboard or mouse would. This means new designs can reuse
existing PS/2 IP cores. Mice and keyboards that use the PS/2 protocol use a two-wire serial bus (clock and data) to
communicate with a host. On the Nexys Video, the microcontroller emulates a PS/2 device, while the FPGA plays
the role of the host. Both the mouse and the keyboard use 11-bit words that include a start bit, data byte (LSB