Introduction 7
CG635 Synthesized Clock Generator
Clock Status and Interface Indicators
10 MHz & SYNTH
In the upper right portion of the front panel are two groups of LED indicators. The upper
group is labeled 10 MHz & SYNTH. This contains the EXT and UNLK LEDs. The EXT
LED indicates that the CG635 has detected an external 10 MHz reference at the 10 MHz
input BNC on the rear panel of the CG635. The CG635 will lock its internal clock to this
external reference.
The UNLK LED indicates that the output has not yet stabilized for some reason. This is
usually due to a user request to change frequency or phase. Frequency changes can take
roughly 30 ms to stabilize. A backward phase step of 360 degrees at 1 Hz can take as
long as 1.5 s to complete. The UNLK LED may also indicate that the internal clock has
not locked to the external reference.
INTERFACE
The lower group of LED indicators is labeled INTERFACE. These LEDs indicate the
current status of RS-232 or GPIB remote programming interfaces. The RS-232 LED is on
if the instrument is configured to accept commands over the RS-232 interface.
Alternately, the GPIB LED is on if the instrument is configured to accept commands over
the IEEE-488 port. When a character is received or sent over one of the interfaces, the
ACT LED will flash. This is helpful when troubleshooting communications problems. If
a command received over the remote interface fails to execute due to either a parsing
error or an execution error, the ERR LED will flash.
