Operation Theory
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59
The mechanism of the SSI/PXI
1.
We adopt master-slave configuration for SSI/PXI. In a system, for
each timing signal, there shall be only one master, and other cards
are SSI slaves or with the SSI function disabled.
2.
For each timing signal, the SSI master doesn’t have to be in a
single card.
For example:
We want to synchronize the A/D operation through the ADCONV
signal for 4 DAQ/PXI-20XX cards. Card 1 is the master, and Card
2, 3, 4 are slaves. Card 1 receives an external digital trigger to start
the post trigger mode a cquisition. The SSI setting could be:
a. Set the SSI_ADCONV signal of Card 1 to be the master.
b. Set the SSI_ADCONV signals of Card 2, 3, 4 to be the slaves.
c.
Set external digital trigger for Card 1’s A/D operation.
d. Set the SI_counter and the post scan counter (PSC) of all
other cards.
e. Start DMA operations for all cards, thus all the cards are
waiting for the trigger event.
When the digital trigger condition of Card 1 occurs, Card 1 will internally
generate the ADCONV signal and output this ADCONV signal to
SSI_ADCONV signal of Card 2, 3 and 4 through the SSI/PXI connectors.
Thus we can achieve 16-channel acquisition simultaneously.
You could arbitrarily choose each of the 6 timing signals as the SSI master
from any one of the cards. The SSI master can output the internal timing
signals to the SSI slaves. With the SSI, users could achieve better
card-to-card synchronization.
Note that when power-up or reset, the DAQ timing signals are reset to use
the internal generated timing signals.
