Maxim Integrated Teridian V.22 bis Linux Softmodem for 73M1822/73M1922 MicroDAA - Manual (Page 62)

V.22 bis Linux Softmodem for 73M1x22 MicroDAA User Guide UG_1x22_043
62 Rev. 1.5
DTMF Tone Detection
The TERIDIAN TSC Softmodem provides two different methods for detecting DTMF tones
being exchanged on the phone line.
1
st
method:
This method is implemented though a specific detection mode enabled by the J6
command. Once the device has entered this mode, the host processor is required to poll
continuously the S65 register in order to detect a valid DTMF tone. It is possible to
increase the polling frequency by disabling the CLI delay in register S73 (ATS73-32). This
method halted by the J0 command requires the device to be off hook.
2
nd
method:
Use of the DTMF based caller ID feature can be exploited to detect DTMF tones. In that
mode, enabled by setting the register S95 (ATS95=48), the decoded DTMF tones are sent
automatically to the host on the RXD lead. This mode does not require the modem to be off
hook, however an AC coupled signal path must be provided from Tip/Ring to RXA (See
Caller ID application note).