Panasonic UF-890 Service Manual page 240

DTMF Tone Generator
The circuit is incorporated in the MODEM on the FCB PC Board. The DTMF tone is conveyed to the
telephone line using the same route as the facsimile signal. The DTMF tone selection is controlled by the
CPU. The relay status during dialing is shown below.
DTMF Tone
PLS Relay
CML Relay
Line release
Line status
break
make
break
make
Speech First
condition
Prepause
break
make
Speech
digit condition
Inter-digit
pause
240
Second Speech
digit
condition
DTMF signal