1-8. BLOCK DIAGRAM PRESENTATION. (CONT)
DUAL TONE MULTIFREQUENCY (DTMF) OSCILLATOR AND KEYSENDER CIRCUIT
This circuit is made up of two transformer-coupled transistor oscillators which are controlled by the contacts of the digit keysender push
button switches. The DTMF oscillator and keysender circuit produces the following outputs:
A burst of 570 Hz ring tone in point-to-point mode.
Dual tone frequencies for digit information, establishing priority, conference, or recall signaling to the switching facility.
EXTENSION CONTROL CIRCUIT
The extension control circuit controls the signals of extension telephones. Its functions include stopping the ring tone in an extension
telephone when the handset of any other extension is lifted from its cradle during the ring cycle. It also stops the release timer in an
extension telephone until the last extension telephone handset is placed in its cradle.