OMNIBUS II FEATURES
an output, the status of a core discrete output can be verified by reading the input.
At power on all core discrete outputs are tristated and are enabled by writing to
the output or by explicitly enabling it.
Ballard’s BTIDriver API provides functions to read, write, and enable (tristate)
the core discretes. The parameter dionum in the API functions
(BTICard_ExtDIORd, BTICard_ExtDIOWr, BTICard_ExtDIOEnWr, etc.)
specifies which discrete to read or write. Table 4.5 shows the mapping between
the external hardware pin and dionum.
A specific sync or trigger can use one or more of the designated core discretes.
After a core discrete has been allocated as a trigger or sync using the enable and
mask parameters in a sync or trigger define API function, the line may no longer
be used as a discrete output or input. More than one core discrete, each with an
individually specified polarity, may be used in combination to define a sync or
trigger state. For instance, a trigger may be defined as a particular state of only
one input, or it may be defined as a particular combination of two or three trigger
inputs. Other triggers and syncs may use the same or different combinations of
these lines. Refer to the BTIDriver software manuals for more information on
programming these discretes and their use as syncs and triggers.
Table 4.5 below shows the correlation between dionum, the output pin, and its
hardware reference designator. The last column shows which of these discretes
may be used as trigger inputs or sync outputs in the BTIDriver API functions.
The names for core discretes are prefixed by CDIO (e.g., CDIO2).
Table 4.5—Hardware versus software designation of core discretes
Processes that are configured to be triggered by an external trigger can be trig-
gered through software using the BTICard_CardTriggerEx function. This is use-
ful for software testing and does not require external trigger equipment.
4.5 Avionics Discretes
The OmniBus II MIL-STD-1553 and ARINC 708 modules (see Sections 6.2 and
6.5) have 16 avionics shunt discretes which can be used to signal and detect
events, determine status, and to drive loads. Each avionics shunt discrete I/O pin
is configured as both a shunt input and a shunt output. When used as an output,
the status of a pin can be verified by reading the input for the pin.
4-4 OmniBus II PCIe/PXIe User’s Manual
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