- July 23, 2008
- US Digital
July 23, 2008 - The USB4 is a data acquisition device designed to record data from 4 incremental encoders, 8 digital inputs and 4 analog input channels. In addition, the USB4 provides 8 digital outputs and 4 analog output channels. The 8 digital outputs also have a latching emergency stop (E-Stop) input. When the E-Stop input is activated, the 8 digital outputs will turn off immediately. The analog input/output channels provide 12-bit data conversions at rates up to 44 kHz per channel.All communication between the USB4 and the host PC is sent over a High-Speed USB 2.0 interface. The USB4 is compatible with USB 2.0 hubs, allowing multiple USB4 units to be used with a single PC. To handle continuous streaming of data over USB to the host PC, the USB4 has a 32 Mbyte FIFO to buffer the captured data when the host PC or USB bus is busy.The digital input port can handle input logic levels from +3V to +25V and the digital output port has open drain MOSFET outputs to switch up to 1A at +25V. The range of the analog input/output channels is 0V to +5V. Four independent, flexible, incremental encoder interfaces are implemented in hardware on the USB4. Each encoder channel has a 24-bit up/down counter that is easily reconfgured for various counting modes such as modulo-N, non-recycle, range-limit and normal counter mode. Quadrature input modes of x1, x2, x4, clock/direction, and indexing modes can also be selected. Each encoder channel can also measure the pulse width and pulse period of its "A" input while simultaneously decoding the quadrature state. This feature allows RPM speed measurements to be made from the encoder input or interfacing to sensors with PWM (pulse width modulated) outputs.The USB4 can capture data once per clock cycle of a user programmable 32-bit clock generator or on every rising or falling edge of the input port pins. Data capture can be programmed to run continuously or to start only when certain conditions are met such as the encoder count matching a certain value, or if the there is encoder movement in a certain direction. Encoder events can also output on the output port to trigger external devices. Trigger conditions can also be set for the analog input and PWM input channels; in addition, the USB4 can be configured to have the input port pins serve as a trigger to start data acquisition. The input port triggering is flexible and allows the user to form the final trigger from a combination of conditions on the input port with up to 2 levels of triggering. For example, trigger1 can be set to a rising edge of bit 0 and bit2, trigger2 can be set to a falling edge on bit3. Data capture will only start if trigger1 occurs first, then trigger2.US Digital provides a CD with all the software and documentation needed to use the USB4. A PC demo application is included, allowing the user to confgure and explore various features of the USB4 using a graphical user interface. A library with a detailed Application Programming Interface is provided so users can develop their own applications; additionally, the CD provides several examples that demonstrate how to use the FIFO, how to log data, etc. For users that prefer lower level control, a register based interface and documentation is provided so the USB4's internal registers can be confgured at the bit level.
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