ZZRT RIT ON/OFF 6600M

What is the command syntax you are sending?

This is not a bug as I have recently learned.  On the M model radios, there is the concept of a "tune mode" which is a mode that the front panel knob is in.  This is either tune the frequency or tune X/RIT.

When you issue the ZZRT1; command to turn on RIT, you have actually enabled RIT mode in the radio.  This is confirmed by issuing the ZZRT; command and getting the ZZRT1; response. 

What you have not done change the tune mode of the M model radio and because of this the RIT indicator light will not be illuminated and tuning the VFO knob will not change the RIT frequency.

What you can, however, do via a CAT command is to set the RIT offset using the ZZRG; command.  When you first enable RIT using the ZZRT1 command, the RIT offset is 0 Hz. The front panel panadapter display will not visually indicate that RIT is enabled if the offset is 0 Hz.  As soon as you change the RIT frequency using the ZZRGxxxxxx; command, you will see the visual indication of RIT on the panadapter.

Use ZZRC; to clear the RIT offset.

XIT has an analogous set of CAT commands that do the same thing.

We plan to update the CAT manual to better explain this behavior and the dependencies when using ZZRT and ZZXG CAT commands.