Digilent PLTW S7 Referenzhandbuch - Seite 6

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PLTW S7 Reference Manual

Oscillators/Clocks

The PLTW S7 includes a 12 MHz crystal oscillator connected to pin M9 (an MRCC input on bank 14). This clock is

intended to be used as a general-purpose system clock. The clock can drive MMCMs to generate clocks of various

frequencies and with known phase relationships that may be needed throughout a design. The 12 MHz input clock

cannot directly drive a PLL because they have a minimum input frequency of 19 MHz. Some rules restrict which

MMCMs and PLLs may be driven by the 12 MHz input clock. For a full description of these rules and of the

capabilities of the Spartan-7 clocking resources, refer to

User Guide".

Xilinx offers the Clocking Wizard IP core to help users generate the different clocks required for a specific design.

This wizard will properly instantiate the needed MMCMs and PLLs based on the desired frequencies and phase

relationships specified by the user. The wizard will then output an easy-to-use wrapper component around these

clocking resources that can be inserted into the user's design. The clocking wizard can be accessed from within the

Vivado and IP Integrator tools.

USB-UART Bridge (Serial Port)

The PLTW S7 includes an FTDI FT2232HQ USB-UART bridge (attached to Micro-USB connector J5) that allows the

user to use PC applications to communicate with the board using standard Windows COM port commands. Free

USB-COM drivers, available from

to UART/serial data. Serial port data is exchanged with the FPGA using a two-wire serial port (TXD/RXD). 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 K15 and L12 FPGA pins.

An onboard status LED (LD6) provides visual feedback on traffic flowing through the port.

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 designs 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 PLTW S7 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 Spartan-7 are shown in Figure 5.1. Signal names that imply

direction are from the point-of-view of the DTE (Data Terminal Equipment), in this case, a PC connected to the

Micro USB port.

Other product and company names mentioned may be trademarks of their respective owners.

Xilinx

Figure 4.1. Clock input.

FTDI's website

under the "Virtual Com Port" or VCP heading, convert USB packets

UG472, titled "7 Series FPGAs Clocking Resources

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