Section 6; Triggering; Overview - VTI Instruments Metek EX1202 User Manual

T
RIGGERING
O
VERVIEW
The EX1200 is a bridge device and, therefore, does not expose a triggerable action. However, for
ease of use, the scanner driver exposes a trigger model which functions like the SCPI 1999 Trigger
Subsystem and works on the device and all installed plug-in cards. The user should be able to
program to this representation except where otherwise noted. This is illustrated in Figure 6-1.
The trigger model is sectioned into five layers: IDLE, INIT, ARM, TRIG, and DEVICE. The
EX1200 system reset condition places it in the IDLE state. A Scanner Initiate() API call begins the
acquisition sequence by transitioning the instrument into the ARM layer. As this occurs, the
reading buffer memory is cleared.
Upon entering the ARM layer, the ARM Count is reset to its specified value. The instrument
remains in the ARM layer until the specified ARM event occurs. Once that occurs the ARM Count
is decremented, and the instrument transitions into the TRIG layer.
The instrument remains in the TRIG layer until the specified TRIG event occurs. Once that occurs,
the instrument transitions into the DEVICE layer.
In the DEVICE layer, channels in the scanlist are measured the requested sample count number of
times, and stored into local memory (FIFO).
If there are more steps in the scanlist, the instrument stays in the TRIG layer until the specified
TRIG event (and subsequent device action) occurs enough times to finish the scanlist. Once the
scanlist is complete, the instrument then evaluates the remaining ARM Count and repeats the
ARM layer action if it is nonzero. However, since each transition into the TRIG layer restarts the
scanlist, each additional ARM layer action results in the full specified number of TRIG Count
actions through the TRIG layer and DEVICE layer.
Once the ARM Count reaches zero, the instrument transitions back into the IIDLE layer. If the
Arm Count is the special value indicating "Infinite", the ARM layer is automatically reentered.
However, unlike with an Initiate() API call, the reading buffer memory is not cleared.
EX1200 Triggering
www.vtiinstruments.com
S
ECTION
6
103