National Instruments Data Acquisition Device NI USB-621x - Manual (Page 136)

© National Instruments Corporation 11-1 NI USB-621x User Manual
11
Bus Interface
The bus interface circuitry of USB-621x devices efficiently moves data
between host memory and the measurement and acquisition circuits.
All USB-621x devices are jumperless for complete plug-and-play
operation. The operating system automatically assigns the base address,
interrupt levels, and other resources.
USB-621x devices incorporate USB-STC2 technology to implement a
Hi-Speed USB interface.
USB Signal Stream
USB-621x devices have four fully-independent USB Signal Streams for
high-performance transfers of data blocks. One USB Signal Stream is
available for each measurement and acquisition block:
• Analog input
• Analog output
• Counter 0
• Counter 1
Data Transfer Methods
The two primary ways to transfer data across the USB bus are USB Signal
Stream and programmed I/O:
• USB Signal Stream—A method to transfer data between the device
and computer memory using USB bulk transfers without intervention
of the microcontroller on the NI device. NI uses USB Signal Stream
hardware and software technology to achieve high throughput rates
and increase system utilization in USB devices.
• Programmed I/O—A data transfer mechanism where the user’s
program is responsible for transferring data. Each read or write call in
the program initiates the transfer of data. Programmed I/O is typically
used in software-timed (on-demand) operations. Refer to the
Analog