VTI Instruments EX1000A - Trigger Event; Retrieving Data (Read FIFO and Streaming Data); Read FIFO

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EX10xxA Programming 113
programmed with a static level of low, the pulse will be high-going. Each pulse generation requires
a separate function. This function accepts a value that represents the channels to be pulsed within
the 8-bit bus, specified in either decimal (0 through 255) or hex (0x00 through 0xFF). Within the 8-
bit field, the MSB corresponds to VTB channel 7 and the LSB corresponds to VTB channel 0.
Example: This code block sets bit 7 to a static level of low and then generates a high-going pulse.
vtex10xxA_set_vtb_output(vi, 0x00);
vtex10xxA_set_vtb_output_enable(vi, 0x80);
vtex10xxA_set_vtb_pulse(vi, 0x80);
TRIGGER EVENT
An acquisition sequence will be conducted once the programmed arm and trigger events are
recognized. In addition to the programmed event sources, software arms and software triggers are
always enabled. These are used to put the trigger model under direct software program control.
A software arm is performed by the vtex10xxA_soft_arm function. The software arm applies at the
time it is issued and will be ignored if the system is not waiting for an ARM event. The issuance of
a software arm has no effect on the ARM source configuration.
A software trigger is performed by the vtex10xxA_soft_trigger function. The software trigger
applies at the time it is issued and will be ignored if the system is not waiting for a TRIG event. The
issuance of a software trigger has no effect on the TRIG source configuration.
RETRIEVING DATA (READ FIFO AND STREAMING DATA)
The EX10xxA stores acquisition data in a large, on-board FIFO in the instruments RAM memory.
14 MB of RAM are reserved for the on-board FIFO. There are two primary mechanisms for
retrieving acquisition data from the EX10xxA FIFO:
 Read FIFO
 Asynchronous Streaming Data
The Read FIFO mechanism is similar to the way data is returned from traditional data acquisition
instruments, with the user application making periodic (polling) queries of the instrument to retrieve
data from the instrument’s on-board FIFO, while asynchronous data streaming is a more modern,
efficient technique, made possible by the instrument’s LXI interface, in which the instrument
automatically transmits acquisition data to the user application as data becomes available.
The streaming data interface is slightly more complicated to use than the Read FIFO interface, but
makes very efficient use of the host PC’s processor and the test system’s network. As such, the
streaming data interface scales well for high channel count and/or high sample rate systems. The
two data retrieval mechanisms are mutually exclusive – if the streaming data interface is enabled,
Read FIFO requests will return an error.
Read FIFO
The EX10xxA utilizes a 14 MB FIFO memory storage to buffer acquisition data prior to retrieval.
The amount of scans that can be buffered within the memory is dependent on the number of channels
in the scan list and the requested data format. See Acquiring Data in Section 3 for specific formulas
and examples. The number of data pages (scans) that have yet to be retrieved from FIFO memory
is obtained using the vtex10xxA_get_fifo_count function.
Figure 6-3 shows the general sequence of events when using the vtex10xxA_read_fifo or
vtex10xxA_read_fifoEx functions. In this diagram, time flows from top to bottom. The two vertical
lines represent the two network nodes: the host PC, running the user application, and the EX10xxA
instrument. The diagonal arrows connecting them represent network messages sent between them