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Cmod A7 Reference Manual

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accessed after configuration (pin E19). This allows access to this pin without having to instantiate the special FPGA

primitive called STARTUPE2.

Xilinx's AXI Quad SPI core can be used to read/write the flash in a MicroBlaze design. Refer to Xilinx's product guide

for this core to learn more about using it, or to Micron's datasheet for the flash device to learn how to implement

a custom controller.

Figure 4.1. Cmod A7 Quad-SPI Flash.

5 USB-UART Bridge

The Cmod A7 includes an FTDI FT2232HQ USB-UART bridge (attached to the Micro-USB connector) that allows

users to 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). 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 J17 and J18 FPGA pins.

An on-board status LED provides visual feedback on traffic flowing through the port: the LED next to DIP pin 25

will blink in response to TX or RX traffic.

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 Cmod A7 to be

programmed, communicated with via UART, and powered from a computer attached with a single Micro-USB

cable.

Warning: When a USB host is attached to the Micro-USB connector, the VU pin on the DIP connector (pin 24) is

driven to the voltage being provided by the USB host (typically between 4.5V-5.5V). If you have a power source

attached to the VU pin, you must disconnect it before attaching a USB host, or risk damaging it. This can be

particularly dangerous if the power source is a battery.