Owner manual

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.

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.

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).