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About Fast Data Channel (FDC) Operation
VX4101A MultiPaq Instrument User Manual
2–15
Before VXIbus instruments can communicate with each other, you must
establish an I/O linkage between the instruments. The complexity of this
communications session varies with the host environment, but typically involves
Operating System calls that return I/O driver reference handles. You must use
both Word Serial Protocol (WSP) as well as Fast Data Channel I/O drivers to set
up, configure, and terminate FDC channels. Only actual data buffer transfers use
the physical FDC channel.
After the WSP and FDC I/O drivers are established between the Commander and
Servant Device (typically a host computer and the instrument), an FDC channel
has to be configured and opened for operation. Configuring the channel defines
the transfer characteristics, such as access protocols, data width, and others.
Opening the channel identifies the particular FDC channel to be used, its
location in shared memory, and its maximum size.
NOTE. Multiple FDC channels may be established concurrently between a
Commander and Servant pair.
Data can be downloaded from the host to the instrument as well as extracted
from the instrument and transferred back to the host. Prior to the actual data
transfer, the host must define the direction of the data transfer. The transfer
operations work as follows:
Transferring Data from the Host to the Instrument. Source instruments are
candidates for FDC data transfers from the host to the instrument. In this
scenario, a buffer of data is transferred from the host application to the instru-
ment for processing.
Data Transfers from the Instrument to the Host. Measurement instruments are
candidates for FDC data transfers from the instrument to the host. In this
scenario, a buffer of data is transferred from the instrument back to the host for
processing.
Bi-Directional Transfers. FDC channels can be bi-directional. For example, some
applications might require retrieval of blocks of data from a source instrument,
transmit blocks of data to a measurement instrument, or repeatedly transmit and
receive data between instruments.
Establishing a
Communications Session
Opening and Configuring
an FDC
Transferring Data Via the
FDC Channel