MC52i/MC55i Auto accept incoming call

Question

I want that my MC52i auto accept an incoming call. If I use AT commands to answer manually (ATA) it works fine, but I'm not able to force the modem auto accepting an incoming call. On other devices it works with ATS0=1 but not on the MC52i. I think it has something to do with the GPRS Mode?

Answer 1

What type of call are you trying to accept, voice or CSD? Setting S0 ought to be enough for this. Try to enable AT+CRC=1 and examine the +CRING: <type> unsolicited result code (see 27.007 for details). Does it fail to auto answer all incoming calls? Try to have it auto answer both voice calls and data calls. Try to call from PSTN, ISDN and mobile phone (both same operator and different operator. Try several different phone models). If it fails to answer all those cases then you probably have to write off auto answer as a possibility. Oh, by the way, also try with several different sim cards (from at least more than one operator) in the modem to rule out problems with the operator/subscription.

I have probably given enough options to tweak so that testing every single combination is not feasible and useful, but pick some variations of all of them and set up at least 20 different test cases.

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Although very unlikely, I'll mention the following for completeness and as a background to one of the many reasons why testing with several different operators is important:

There could be a problem if the network does not include call type information in the Bearer Capability in the SETUP message and then the phone does not know how to answer the call. This is very unlikely today, but several years ago some network could behave so. Because of this the phones used to have a "receive next call as" configuration to determine how to behave then. But I assume all newer phones to just ignore this scenario (It was applicable back in the days when Ericsson made mobile phones in their own brand, at least I remember seeing seeing this configuration option in their single menu style phones like T28. I do not remember if it survived the conversion to the icon based menus).