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1281A
User Manual
Sequence Advance
Modes
As shown above, sequences are built as simple table of which
define link, segment, loops and advance bits. When placed in
sequenced mode, the output is changing from link to link in an
ascending order. The term Sequence Advance Modes defines what
is causing the instrument to step from link to link. There are four
basic advance modes that can be selected for the sequence mode:
Auto, Stepped, Single, Repeated Single and mixed. These modes
are explained in the following paragraphs. Also note that there are
some limitations that should be observed while using the various
sequenced advance modes. These limitations are summarized in
Table 1-4.
Auto
Auto advance sequence is the mode that you want to use when the
sequence is expected to run continuously from the first step in the
table to the last, and then resume from the first step. There are no
interrupts between steps and between the last and the first step of
the sequence. When auto mode is selected, the 1281A can also be
placed in triggered and gated run modes.
Stepped
Stepped advance sequence is the mode that you want to use when
the sequence is expected to advance on triggers only. The trigger
source is selectable from either external or bus commands. The
step will run continuously until a trigger advances the sequence to
the next step. When the last step is reached, the next trigger will
advance to the first step in the sequence and this sequence will
repeat itself as long as triggers are applied to the generator. Note
that the generator operates in continuous run mode; Trying to place
it in trigger or gated run mode will issue a settings conflict error
message.
Single
Single sequence advance is the mode that you want to use when
the sequence is expected to advance on triggers only. This mode
operates in conjunction with the trigger mode only. An attempt to
select the SING advance mode when the 1281A is in continuous
operating mode will generate an error. In single advance mode, the
generator idles between steps until a valid trigger signal is sensed.
After trigger, the generator outputs one waveform cycle and jumps
to the next sequence step. If loops (repeats) were programmed, the
output will repeat itself for the programmed number of loops and
then will jump to the next sequence step.
Repeated Single
This mode operates in conjunction with the trigger mode only. An
attempt to select the SING advance mode when the 1281A is in
continuous operating mode will generate an error. In repeated
single advance mode, the generator idles between steps until a
valid trigger signal is sensed. After trigger, the generator outputs
one waveform cycle. If loops (repeats) were programmed, the
output will repeat this segment every time a trigger is received. Only
after executing all of the programmed loops will the sequence step
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