Answering Circuit Switched Data ( CSD ) calls

ISSUE:
When receiving inbound Circuit Switched Data (CSD) the modem answers all calls in voice mode rather than data mode.

Additionally, if AT+CRC=1 has been set the modem when receiving a call indicates +CRING: 0 (0 indicates voice call.)

SOLUTION:
#1 Verify with carrier the cellular account has Circuit Switched Data active.

#2. In order for the modem to answer inbound Circuit Switched data calls issue one of the following two commands:

AT$QCVAD=3
Modem will answer next call in async data mode (10 minute timeout)

AT$QCVAD=4
Modem will answer all calls in async data mode

#3 To answer call you can either issue command ATS0=2 to have modem answer calls automatically after two rings or issue command ATA when inbound call is indicated by device.

ADDITIONAL NOTES
A. To once again answer calls in voice mode issue command AT$QCVAD=0

B. ATS0 and AT$QCVAD commands will be reset to default values of 0 (auto answer off and answer calls in voice mode) when the command AT&F is issue or when power is lost.

It is not possible to store different values for the ATS0 and AT$QCVAD commands. If the AT&F command is sent to the device or power is lost to the device you must reissue the ATS0 and AT$QCVAD commands if you desire to answer calls automatically or answer calls in data mode.