HP 81101A Reference Manual page 69

Example
To set up the external PLL reference:
:ROSC:SOUR EXT
:ROSC:EXT:FREQ 10 MHZ
Command
:ROSC:EXT:FREQ
Long
[:SOURce]:ROSCillator:EXTernal:FREQuency
Form
Set & Query
Parameter Numeric
*RST value
5 MHz
Specified limits
5 MHz or 10 MHz
Description
Use this command to set/read the expected reference frequency for the
PLL at the CLK-IN connector. The external reference can be a 5 or
10 MHz signal. Note that if you program any value other than the two
specified values, the value will be set to the nearest of the two specified
values.
Example
To set up the external PLL reference:
:ROSC:SOUR EXT
:ROSC:EXT:FREQ 10MHZ
Programming Reference
SCPI Instrument Command List
Set external PLL reference (CLK-IN)
Set expected PLL reference frequency to
10 MHz
Set external PLL reference (CLK-IN)
Set expected PLL reference frequency to
10 MHz
69