Keithley 2002 User Manual page 62

Idle
The instrument is considered to be in the idle state whenever
it is not operating within one of the three layers of the Trigger
Model. The front panel ARM indicator is off when the instru-
ment is in the idle state. While in the idle state, the instrument
cannot perform any measurement or scanning functions.
From the front panel there are four ways to put the instru-
ment into idle:
• Select RESET GPIB from the SAVESETUP option of
the main menu. Press the TRIG key to take a reading.
After each reading, the instrument returns to the idle
state.
• Select HALT from the CONFIGURE TRIGGER menu.
Press the TRIG key to resume triggering.
• Enable BURST-MODE from the CONFIGURE DATA
STORE menu. This places the instrument in idle until
the TRIG key is pressed. After each burst acquisition
the instrument returns to idle.
• Configure an internal or external scan with the SCAN
key. Disabling the scan resumes triggering.
Trigger Model Layers
As can be seen in Figure 2-12, the trigger model uses three
layers: the Arm Layer, Scan Layer and Measure Layer. For
IEEE-488 bus operation, these layers are known as Arm Lay-
er 1, Arm Layer 2 and the Trigger Layer.
Once the Model 2002 is taken out of the idle state, operation
proceeds through the layers of the trigger model down to the
device action where a measurement occurs.
Control Sources — In general, each layer contains a control
source which holds up operation until the programmed event
occurs. The control sources are described as follows:
• Immediate — With this control source selected, event
detection is immediately satisfied allowing operation to
continue.
• Manual — Event detection is satisfied by pressing the
TRIG key. Note that the Model 2002 must be taken out
of remote before it will respond to the TRIG key. Press-
ing LOCAL or sending LOCAL 716 over the bus takes
the instrument out of remote.
• GPIB — Event detection is satisfied when a bus trigger
(GET or *TRG) is received by the Model 2002.
• RT-Clock — Event detection in the Arm Layer is satis-
fied when the programmed time and date occurs. The
real-time clock control source is not available in the
Scan Layer and Measure Layer.
• Timer — Event detection is immediately satisfied on
the initial pass through the layer. Each subsequent
detection is satisfied when the programmed timer inter-
val (1 to 999999.999 seconds) elapses. A timer resets to
its initial state when operation loops back to a higher
layer (or idle). Note that a timer is not available in the
Arm Layer.
• External — Event detection is satisfied when an input
trigger via the EXTERNAL TRIGGER connector is
received by the Model 2002.
• Triglink — Event detection is satisfied when an input
trigger via the TRIGGER LINK is received by the
Model 2002.
• Hold — With this selection, event detection is not satis-
fied by any of the above control source events and oper-
ation is held up.
Source Bypasses — As can be seen in the flowchart, each
layer has a path that allows operation to loop around the con-
trol source. Each path is called a source bypass.
When a source bypass is enabled, and the external or trigger
link (triglink) control source is selected, operation loops
around the control source on the initial pass through the lay-
er. If programmed for another event detection in the layer,
the bypass loop will not be in effect though it is still enabled.
The bypass loop resets (be in effect) if operation loops back
to a higher layer (or idle).
In the Arm Layer and Scan Layer, enabling a source bypass
also enables the respective output trigger. In the Trigger Lay-
er, its output trigger is always enabled and occurs after every
device action. See Output Triggers for more information.
Delays — The Scan Layer and the Measure Layer have a
programmable delay (0 to 999999.999 seconds) that is en-
forced after an event detection.
Device Action — The primary device action is a measure-
ment. However, the device action could include a function
change and a channel scan (if scanner is enabled). A channel
is scanned (closed) before a measurement is made. When
scanning internal channels, the previous channel opens and
the next channel closes (break-before-make). Also included
in the device action is the internal settling time delay for the
relay.
Output Triggers — In the Arm Layer and Scan Layer the
output triggers are enabled only if their respective source by-
passes are also enabled. If a trigger link (triglink) control
source is selected, the output trigger pulse is available on the
selected TRIGGER LINK output line. For all other control
Front Panel Operation
2-45