H A R D W A R E O P E R A T I O N
Data Device Corporation
BU-65570/2i Manual
29
Monitor DMA to Host Buffer
The BU-65572iX is fully compliant to the PCI standards for both Target
and Master applications. As a PCI master, the BU-65572iX 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 32K 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 accessable to the application. All
operations that will be performed on the DMA buffer must be made
through the appropriate RLT routines.
Software Control Of Bus Configuration
The BU-65572iX 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 37.5 ohms. A setting of Half will cause a bus
termination of 75.0 ohms. This control makes it quite simple to connect
the BU-65572iX 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 software functions provided in the ‘C’
library which control relays for each installed channel.
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