1-9. OPERATIONAL MODES AND CONTROLS. (CONT)
EXTENSION CONTROL MODE
The functions of the extension control circuit depend upon whether the telephone set is the controlled or controlling telephone. The
controlling telephone is the first of a set of extension telephones to be lifted from the cradle and the last to be replaced in the cradle.
The first telephone lifted from the cradle stops the ringing and the seize tones of the other telephones. When a number of telephones
have their handsets removed from their cradles at the same instant, multiple seize tones are sent.
If there is no control signal from any extension telephone, any telephone will send seize tones and release tones for each off-cradle and
on-cradle condition, no matter what the previous circuit condition was.
Battery ground is common between extension telephones by way of the receive pair of wires.
When a number of telephone handsets are lifted from their cradles, any one telephone can send digit selection frequencies.