QuickUSB FAQ

• How long does it take to change the state of an I/O pin on the QuickUSB Module?

For a hi-speed connection, the time needed to change the state of a general purpose I/O pin on the module is approximately 200 microseconds. For a full speed connection the time is slightly more than 1 millisecond.

• How do it connect up an FPGA to QuickUSB?

There are two basic I/O models for connecting an FPGA to QuickUSB: GPIF master and slave FIFO mode. Put simply, in GPIF master mode, the PC (via QuickUSB) controls and transfers data to or from FIFOs that you instantiate inside the FPGA and in slave FIFO mode, the FPGA works independently of the PC and transfers data to or from the QuickUSB internal FIFOs when it needs to. For more details, consult the QuickUSB User Guide v2.00.

• How do I power my circuit from QuickUSB?

QuickUSB supplies unregulated +5V at up to 250 mA (max) on the VBUS pins. For modules Rev A1 and above, an FET on the QuickUSB module controls power. Power is off by default and then turned on once the host (per the USB specification) configures the module. The QuickUSB module incorporates a current limiting circuit that will shut down the VBUS pins on an over current condition. In addition the entire module may be powered down by the host or a USB hub if it draws more than the 500 mA allotted by the USB.

If your circuit draws less than 250 mA, you may power it from the unregulated 5V provided on the VBUS pins. However, if your circuit will draw more than 50 mA, you should design your circuit with either a downstream power switch (such as the TPS2051A) if you need unregulated 5V or an active high enable logic switched voltage regulator if you are going to regulate VBUS. Connect the enable signal to SW_PG (pin 76). This signal will enable your circuit’s voltage regulator once the VBUS switch is turned on and the output voltage has stabilized to >= 93% of the voltage supplied by the USB. For more information about the QuickUSB VBUS switch, consult the datasheet for the Texas Instruments TPS2150.

If your circuit draws more than 250 mA, do not power it from VBUS. It should be powered with an external power supply and connect the digital ground of your circuit to GND. In this case, you might want to connect an unused I/O pin to the external power supply through a current limiting resistor (10K) so you can read the pin to determine the state of the external power supply.

• How should I connect the High-Speed Parallel Port?

The connections that are needed depends on the type of I/O model you select. The I/O models and the details for which connections you need are given in detail in the QuickUSB User Guide v2.00.