IEEE-488 Reference
4-25
:SYSTem:PRESet command also selects the Immediate con-
trol source.
With the Bus control source selected (:TRIGger :SOURce
BUS), the instrument will wait until a bus trigger is received
(GET or *TRG). With the External control source selected
(:TRIGger:SOURCE EXTernal), the instrument will wait
until an input trigger (via EXTERNAL TRIGGER connector
on rear panel) is received. With the Trigger Link control
source selected (:TRIGger:SOURce TLINk), the instru-
ment will wait until an input trigger is received (via TRIG-
GER LINK). With the Hold control source selected
(:TRIGger :SOURce HOLD), the instrument will not re-
spond to any of the control source events.
NOTE
With the Immediate trigger source select-
ed, a “trigger ignored” message will be
displayed if an external trigger is sent to
the Model 2001 or a manual trigger (ie.,
pressing TRIG key) occurs. The external
or manual trigger is not used (ignored).
After the programmed measure event is detected, the instru-
ment will wait for the programmed Delay to time out. The
:TRIGger:DELay <num> command is used to set the Delay
(where num = 0 to 999999.999 seconds).
The *RST and :SYSTem:PRESet commands set the Delay to
zero seconds.
As can be seen in the flowchart, there are three paths that al-
low operation to loop around the control source. Two of these
paths also loop around the Delay. These three paths are de-
scribed as follows:
1. When the Source Bypass is enabled (:ARM :TCONfig-
ure:DIRection SOURce) and the External or Trigger
Link control source is selected, operation will loop
around the control source on the initial pass through the
trigger layer. If programmed to perform another mea-
surement, (measure count > 1), the bypass loop will not
be in effect even though it will still be enabled. The
Source Bypass loop will reset (be in effect) if operation
goes back to arm layer 2.
2. Each time the :TRIGger:IMMediate command is sent,
operation will loop around the control source and the
Delay. It is used when you do not wish to wait for a pro-
grammed measure event to occur (or when the Hold
control source is selected).
3. Each time the :TRIGger:SIGNal command is sent, oper-
ation will loop around the measure control source. This
path functions the same as :TRIGger:IMMediate except
that it does not loop around the Delay.
At this point a measurement will be performed (Device Ac-
tion). Note that 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 taken. When
scanning channels, the previous channel will open and the
next channel will close (break-before-make). Also included
in the Device Action is the internal settling time delay for the
relay.
After a channel is scanned, an Output Trigger will occur. If
the measure control source is programmed for Immediate,
Manual, Bus or Timer, the output trigger pulse will be avail-
able at the METER COMPLETE connector. If the Trigger
Link control source is selected, Output Trigger action will
occur as follows:
1. If the asynchronous Trigger Link mode is selected, the
output trigger pulse will be available on the pro-
grammed TRIGGER LINK output line.
2. If the semi-synchronous Trigger Link mode is selected
and the Source Bypass is disabled (:trig :tcon:dir acc),
the Trigger Link line will be released (goes high).
3. If the semi-synchronous Trigger Link mode is selected
and the Source Bypass is enabled (:trig :tcon:dir sour),
the Trigger Link line will be pulled down low and then
released.
NOTE: See paragraph 3.7.7 for details on using the Trigger
Link.
After the Device Action and an output trigger occurs, the in-
strument will (if programmed to do so) return to the begin-
ning of the trigger layer to perform another measurement.
The :TRIGger:COUNt <n>|INFinite command is used to
set the measure count to a finite value (where n = 1 to 99999)
or for continuous measurements (INFinite). The *RST and
:SYSTem:PRESet commands set the measure count to one.
4.8 General bus commands
General bus commands are those commands such as DCL
that have the same general meaning regardless of the instru-
ment. Commands supported by the Model 2001 are listed in
Table 4-3 which also lists BASIC statements necessary to
send each command. Note that commands requiring that a
primary address be specified assume that the primary address
is set to 16. This is the address that is set at the factory.
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