Astronics OMNIBUS II NI PXIe, User Manual

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OMNIBUS II FEATURES
OmniBus II NI PXIe User Manual 4-3
The OB2 can also be the source of the system synchronization references (IRIG
PCM, IRIG AM, PPS, 10 MHz). In this case, you can set the core timer and tune
the protocol clock frequency using the
BTIDriver API functions. In some cases,
the TSM can synchronize to an input signal and output a different reference signal.
Table 4.1 lists the valid input and output combinations. IRIG output and (Pulse-
Per-Second) PPS output are not available simultaneously.
Drift Input Time Input 10 MHz Out IRIG Out PPS Out
None None Valid Valid Valid
None IRIG Valid - Valid
None PPS Valid - -
10 MHz None - Valid Valid
10 MHz IRIG - - Valid
10 MHz PPS - - -
IRIG IRIG Valid - Valid
PPS None Valid Valid Valid
PPS IRIG Valid - Valid
PPS PPS Valid - -
Table 4.1—I/O Combinations for System Synchronization
The TSM logic is activated only in Core A of an OB2 family device and all TSM
configuration API calls must be directed to Core A.
BTICARD_TSM<*> functions
are used to configure the TSM, but
BTICard_IRIG<*>
functions are supported
for backwards capability. However,
BTICard_IRIG<*>
functions do not allow
drift control or IRIG/PPS pin selection. BTICard IRIGConfig uses the pins
as follows:
Timing Protocol Core/Pin
PPS/PCM IRIG Core A Pin 17
AM IRIG Core B Pin 17
Table 4.2— Pinout Supported by BTICard_IRIG
4.3.1 Core Timer
The OB2 devices internally use a binary system timer that is free-running and
keeps time until either set by software or synchronized to an IRIG signal when
configured as a slave. This system timer is also the source for the IRIG interface
when configured as a master. The system timer has a resolution down to one ns,
but a precision of 10 ns. You cannot change the resolution from one ns, however,