VXI VT1422A - Manual (Page 189)

Creating and Running Algorithms 187 Chapter 6
Input Channels
Input channel identifiers can only appear on the right side of assignment
operators. It doesn't make sense to output values to an input channel. Other
than that, they can appear anywhere other variables can appear. Examples:
dig_bit_value = I108.B0; retrieve value from Input
Channel Buffer element 8, bit 0
inp_value = I124;
retrieve value from Input
Channel Buffer element 24
rscu_value = I12422;
retrieve value from RSCU
Channel Buffer element 2422
O156 = 4 * I124;
retrieve value from Input
Channel Buffer element 24,
multiply by 4 and send result to
Output Channel Buffer element
56
writefifo(I124);
send value of input channel 24 to
FIFO buffer
Defined Input and Output
Channels
Algorithms "reference" channels. They can reference input or output
channels. But, in order for these channels to be available to an algorithm,
they must be "defined." What this means is that an SCP or RSCU must be
installed and an appropriate SOURce or SENSe:FUNCtion must explicitly
(or implicitly, in the case of VT1531A and VT1532A SCPs) be tied to the
channels. If an algorithm references an input channel identifier that is not
configured as an input channel or an output channel identifier that is not
configured as an output channel, the driver will generate an error when the
algorithm is defined with ALG:DEF.
Accessing Remote
Scan Status
Variables
Two remote scan status variables exist for each VT1539A SCP. The variable
syntax is "S1<xx>" where <xx> can be one of 00, 01, 08, 09, 16, 17, 24, 25,
32, 33, 40, 41, 48, 49, 56, and 57. These values are sixteen possible on-board
channels for VT1539A SCPs. These variables are treated as input channels
and can only be read from, not written to. The returned value represents the
operational status of the RSCU connected to the SCP channel.
The possible values are: 0 = normal operation, 1 = RSCU cable disconnected
after INIT and 2 = RSCU scan list is out of synchronization (scan trigger
problem during RSCU’s scan).
Runtime Remote
Scan Verification
For most data acquisition and control applications, it is necessary to know
that the data acquired via an RSCU is not corrupted at runtime. Though the
VT1422A/RSCU system is designed to be very robust and will normally
acquire reliable data, there is a possibility that remote data can be corrupted
in the following ways:
•
The remote box (RSCU) may lose power after a scan is initialized.
•
The cable to the remote box may become disconnected or damaged
during the scanning process.
•
The multiplexer in the remote box may lose synchronization with the
host VT1422A due to false or missing triggers.
For all of the above conditions, the VT1422A/RSCU system should report
the existence of corrupted data immediately to the host system.