IEEE-488 Reference
3-20
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 Arm Layers 1 and 2, the output trig-
gers are enabled only if their respective source bypasses are
also enabled. If a TLINk control source is selected, the out-
put trigger pulse is available on the selected TRIGGER
LINK output line. For all other control source selections, the
trigger pulse is available at the METER COMPLETE con-
nector.
In the Trigger Layer, the output trigger is always enabled and
occurs after every device action. If the control source is set
for EXTernal, IMMediate, MANual, BUS or TIMer, the out-
put trigger pulse is available at the METER COMPLETE
connector. If the TLINk control source is selected, output
trigger action occurs on the selected TRIGGER LINK output
line as follows:
• If the asynchronous Trigger Link mode is selected, the
output trigger pulse is available on the programmed
output line.
• If the semi-synchronous Trigger Link mode is selected
and the source bypass is disabled (:trig:tcon:dir acc),
the Trigger Link line is released (goes high).
• If the semi-synchronous Trigger Link mode is selected
and the Source Bypass is enabled (:trig:tcon:dir sour),
the Trigger Link line is pulled down low and then re-
leased.
Counters — All three layers use programmable counters
which allow operation to return to or stay in the respective
layer. For example, programming the Trigger Layer counter
for infinity (:trig:coun inf) keeps operation in the Trigger
Layer. After each device action and subsequent output trig-
ger, operation loops back to the Trigger Layer control source.
A counter resets when operation loops back to a higher layer
(or idle).
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