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NI Digital System Development Board User Manual
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© National Instruments
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The SD slot is powered from 3.3 V, but is connected through MIO Bank 1/501 (1.8 V).
Therefore, a TI TXS02612 level shifter performs this translation. The TXS02612 is actually
2-port SDIO port expander, but only its level shifter function is used. Mapping out the correct
pins and configuring the interface is handled by the DSDB board definition file.
Both low speed and high speed cards are supported, the maximum clock frequency being
50 MHz. A Class 4 card or better is recommended.
Refer to
microSD Boot Mode
for information on how to boot from an SD card. For more
information, consult the Xilinx Zynq TRM (ug585).
USB HID Host
The Auxiliary Function microcontroller (Microchip® PIC24FJ128) provides USB HID host
capability. Firmware in the microcontroller can drive a mouse or a keyboard attached to the type
A USB connector at J9 labeled “USB HID”. The PIC24 then emulates a PS/2 device towards the
FPGA over two PS/2 ports. Port 0 is always keyboard, while port 1 is always mouse. Hub
support is not currently available, so only a single mouse or keyboard can be used at any time.
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 re-use 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
DSDB, 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 first),
odd parity, and stop bit, but the data packets are organized differently, and the keyboard interface
allows bidirectional data transfers (so the host device can illuminate state LEDs on the
keyboard). Bus timings are shown in Figure 5.
Table 7.
USB HID Pinout
Function
Schematic Net
FPGA Pin
PS/2 Keyboard
Data
PS2_DATA0
R7
Clock
PS2_CLK0
Y11
PS/2 Mouse
Data
PS2_DATA1
Y21
Clock
PS2_CLK1
U11