H A R D W A R E O P E R A T I O N
Data Device Corporation
34
BU-65572T Manual
7.7.4 Monitor DMA to Host Buffer
The
BU-65572T
is fully compliant to the PCI standards for both Target
and Master applications. As a PCI master, the
BU-65572T
is capable of
performing DMA block data transfers from the monitor buffers on the
card to a user buffer in the host memory. This will allow the transfer of
data without interrupting the host processor, enabling it to perform other
more important tasks.
When the application calls the „ddcEnableDma‟ routine, the size of the
DMA buffer must be specified. The DMA buffer size must be greater than
64K words. If it is not greater than this size, then the routine will return
with an error. If the size of the DMA buffer is too large, than the system
will not be able to allocate it and again the routine will fail. Since this
buffer is dynamically allocated from non-swappable system resources,
the DMA buffer size should not be too large. The buffer size can affect
system operation if too much memory is requested.
The DMA buffer is not directly accessible to the application. All
operations that will be performed on the DMA buffer must be made
through the appropriate RLT routines.
7.7.5 Software Control of Bus Configuration
The
BU-65572T
has the capability of being connected to the bus as
either Transformer Coupled or Direct Coupled. Transformer coupling
enables the card to be connected to the 1553 bus with a long stub of up
to 20 feet. Direct coupling requires that the card be connected to the
1553 bus by a stub of no more than 1 foot. The coupling configuration is
dynamically configurable via functions provided in the „C‟ library. Relays
on the board are used to select the correct signal path, direct or
transformer coupled for each of the installed channels.
This card also has the capability of modifying the bus termination to one
of three different loads. If the bus termination is set to None, then the
effective impedance is infinite ohms. If the bus is set to Full, then the bus
termination will be 35 ohms. A setting of Half will cause a bus termination
of 70 ohms. This control makes it quite simple to connect the
BU-65572T
directly to another 1553 device without the need of an external load. As
with the bus coupling mode, the bus termination mode is dynamically
configurable via softwar
e functions provided in the „C‟ library which
control relays for each installed channel.
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