I need to disable the dialing tone on my SIM800L and for that I need to know if the receiving end has answered the call. AT+CPAS returns 4 which stands for 'in progress' both during conversation as well as during the tone before the call is answered so it's of no use.
Is there a way using AT commands? Or should I resort to doing some singal analisis of the output audio? Is there any other device that does have this capability?
The command you are looking for is +CLCC. It is a standard ETSII command, so you will find it in every cellular modem. For the present answer I will refer to the SIM800 AT command guide.
Execution command AT+CLCC list the status of the current calls. For each call you will get a row such as
+CLCC: <id1>,<dir>,<stat>,<mode>,<mpty>[,<number>,<type>,<alphaID>
where:
| Parameter | Description | Values |
|---|---|---|
<idx> |
Call identification number | [1-7] |
<dir> |
Direction | 0 Mobile originated (MO) call 1 Mobile terminated (MT) call |
<stat> |
State of the call | 0 Active 1 Held 2 Dialing (MO call) 3 Alerting (MO call) 4 Incoming (MT call) 5 Waiting (MT call) 6 Disconnect |
<mode> |
Bearer/tele service | 0 Voice 1 Data 2 Fax |
<mpty> |
Multiparty status | 0 Call is not one of multiparty (conference) call parties 1 Call is one of multiparty (conference) call parties |
<number> |
Remote peer phone number (String to be included in quotation marks; phone number in format specified by <type>) |
|
<type> |
Type of address | |
<alphaId> |
Alphanumeric representation of <number> corresponding to the entry found in phone book (String type to be included in quotation marks) |
Usually there is only one call, but anyway you'll be able to determine the call of your interest by checking the number field of the answer.
The <stat> field of the response provides what you need. In fact, it will contain the status of the current call showing a different value between when the modem is dialing (2, in case of Mobile Originated call) and when the call is active (0; also 1 if you want to include held calls).