VTI Instruments EX1000A, User Manual

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EX10xxA Triggering 71
The trigger model is sectioned into five layers: IDLE, INIT, ARM, TRIG, and DEVICE. The
EX10xxA reset condition places it in the IDLE state. A trigger initialize command begins the
acquisition sequence by transitioning the instrument through the INIT layer into the ARM layer. As
this occurs, the reading buffer memory is cleared, and all enabled limit events are reset to their
default states.
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 or a Software Arm is issued. Once that
occurs, the specified ARM Delay is waited, the ARM Count is decremented, and the instrument
transitions into the TRIG layer.
Upon entering the TRIG layer, the TRIG Count is reset to its specified value. The instrument
remains in the TRIG layer until the specified TRIG event occurs or a Software Trigger is issued.
Once that occurs, the specified TRIG Delay is waited, the TRIG Count is decremented, and the
instrument transitions into the DEVICE layer.
In the DEVICE layer, the scan list is measured, calibrated, and stored into local memory. In addition,
limit evaluation is conducted, and enabled limit event states are updated.
If the TRIG Count remains nonzero, the instrument stays in the TRIG layer until the specified TRIG
event (and subsequent device action) occurs enough times to decrement it to zero. Once the TRIG
Count reaches zero, 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 resets the TRIG
Count, 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 INIT layer. If Init
Continuous mode is enabled, the ARM layer is automatically reentered without the issuance of a
trigger initialize command. However, unlike with a trigger initialize, enabled limit events are not
reset, and the reading buffer memory is not cleared. Conversely, if Init Continuous mode is disabled,
the instrument is returned to the IDLE layer and requires the issuance of a new trigger initialize
command to begin a new acquisition sequence.
E
VENTS
There are two events that control the progress through the trigger model: the ARM event and the
TRIG event. Each of these events can be programmed independently to be activated from any
combination of the Trigger Bus, Digital I/O port, LAN events, internal system timer, and LXI alarm.
In addition, the Trigger Bus, Digital I/O port, and timer can be programmed to be Immediate,
creating a permanent satisfaction of the event monitor. Each event monitor can also be bypassed on
command with the issuance of a Software Arm or Software Trigger, as appropriate. Software Arms
and Software Triggers are always enabled, regardless of the other programmed event sources.
The Digital I/O port and the Trigger Bus monitor the digital hardware ports on the rear panel of the
instrument. An event can be controlled by any combination of the eight channels of each port.
Moreover, each channel can be independently programmed to monitor a transition edge or a level.
LAN Events are triggered through the eight LAN Event channels via Ethernet packets
(UPD/multicast or TCP messages). They are configured in a manner similar to the Digital I/O port
and Trigger Bus. These events can occur in “past time”, “now”, or “future time”. “Past time” events
have an IEEE 1588 time that occurred in the past. They function essentially as an immediate (or
“now” event), but, unlike the “Now” event, provide both sent and received information for
debugging purposes. “Now” events have a IEEE 1588 time of “0”, indicating that the event will
occur immediately after it is received). Because they have a time of “0”, the event log will only
identify when this event was received. “Future time” events have an IEEE 1588 time that has not
yet occurred. Because these events occur in the future, they can be prepared for an provide a better
response time than either “past” or “now” events. For more information on LAN Events, please see
the
LAN Events Menu in Section 4.