22.8.2018
Cmod S7 Reference Manual [Reference.Digilentinc]
https://reference.digilentinc.com/reference/programmable-logic/cmod-s7/reference-manual
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The Cmod 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
FTDI's website
under the “Virtual Com Port” or VCP heading, convert USB packets 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 netirely independant 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 Cmod 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.
Figure 5.1 USB-UART Bridge
The Cmod S7 includes one RGB LED (), 4 individual LEDs, and 2 push buttons, as shown in Figure 6.1. The push buttons 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 button was inadvertently defined as an output). The buttons are “momentary” switches that normally generate a low output
when they are at rest, and a high output only when they are pressed.
The four individual high-efficiency LEDs are anode-connected to the FPGA via 330 Ohm resistors, so that they will turn on when a
logic-high voltage is applied to their respective I/O pins. Additional LEDs that are not user-accessible indicate power-on, FPGA
programming status, and USB-UART traffic.
The single RGB LED () has three input signals that drive the cathodes of three smaller internal LEDs: one red, one blue, and one green.
Driving the signal corresponding to one of these colors low will illuminate the internal LED (). The RGB LED () will emit a color
dependent on the combination of internal LEDs that are currently being illuminated. For example, if the red and blue signals are driven
low and green is driven high, the RGB LED () will emit a purple color.
Note: Digilent strongly recommends the use of pulse-width modulation (PWM) when driving the RGB LED (). Driving any of the
signals to a steady logic '0' will result in the LED () being illuminated at an uncomfortably bright level. This can be avoided by ensuring
that none of the RGB signals are driven with more than a 50% duty cycle. Using PWM also greatly expands the potential color palette of
the RGB LED (). Individually adjusting the duty cycle of each each color between 50% and 0% causes the different colors to be
illuminated at different intensities, allowing virtually any color to be displayed.
Figure 6.1 shows how each of the LEDs and push buttons are connected to the Spartan-7.
5 USB-UART Bridge (Serial Port)
6 Basic I/O
