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VX4101A MultiPaq Instrument User Manual
2–13
About Fast Data Channel (FDC) Operation
The following section tells you about using the Fast Data Channel (FDC), a
high-speed protocol for data transfer, with the VX4101A MultiPaqtInstrument.
The VXIplug&play driver provided with the VX4101A implements FDC and
does not require full knowledge of the protocol. The description that follows is
only for users who choose not to use the driver.
NOTE. For more information on using VXIplug&play drivers to implement FDC,
see the online help files accompanying the driver software.
About FDC
Fast Data Channel (FDC) is a communications protocol for transferring data
between a VXIbus Commander device and its Servant device. The protocol is
standardized, approved by the VXIbus Consortium in a standard known as
VXI-10. It is supported by VXIbus instrument hardware and software vendors.
FDC was recognized as a supported protocol by the VXIplug&Play Alliance in
1996.
FDC is a bi-directional, block oriented, data transfer mechanism that uses shared
memory and is well suited for transferring large buffers of data between a host
and a servant device. Bit flags in the FDC header word allow transfer of data
larger than the FDC buffer memory. Drivers supporting the protocol must exist
on each Host/Servant pair employing FDC.
The FDC protocol defines the establishing of FDC channels, setting up and
coordinating of the data transfers, channel termination, and error handling. In
order to use the FDC protocol for accessing instrumentation data, you must use
your application code to establish FDC channels, invoke FDC I/O drivers to
actuate the data transfer, close the the channels at termination, and handle any
errors that resulted from the data transfer. Vendor supplied I/O libraries are
generally required.
The FDC Process
In a typical VXIbus instrumentation system, the Commander device is your host
computer, and the Servant device is the instrument. A typical user test applica-
tion employing FDC would contain many of the following operations:
1. Establish a communication session with the instrument