HP 81101A Reference Manual page 41

Command
:ARM:PER
Long
:ARM[:SEQuence[1]|STARt][:LAYer]:PERiod
Form
Set & Query
Parameter
Numeric
Parameter Suffix
S or SEC with engineering prefixes.
10.00 µs
*RST value
Specified Limits
20 ns to 999.5 s
Description
Use this command to program the period of the PLL (INTernal2) when it
is used as the :ARM:SOURce for internal triggering of pulses, bursts or
patterns.
If you are using the PLL as :TRIGger:SOURce use the
[:SOURce]:PULSe:PERiod command to set the pulse period.
Example To set up bursts of four 50 ns pulses occurring every 500 ns:
:TRIG:SOUR INT
:PER 50 NS
:ARM:SOUR INT2
:ARM:SENS EDGE
:ARM:PER 500ns
:ARM:TRIG:COUNT 4
Programming Reference
SCPI Instrument Command List
Select internal osc.as pulse period source
Set pulse period to 50 ns
Select PLL as triggering source
Sense edge of PLL signal
Set triggering period to 500 ns
Set burst length to 4
41