SIM900 data to command mode using DTR

[aderregibus]

Hello,

I am using the SIM900 to establish a GPRS connection using PPP protocol over serial port.
That is working perfectly.
But I want to use the DTR pin to switch from data mode to command mode in order to send a few AT commands and then return to data mode again.

I am configuring DTR with AT&D1.
I am also configuring AT+CSCLK=0 to avoid entering sleep mode with DTR.

My problem is that I need to wait for at least 2 or 3 seconds, after pulling DTR low and then high again, before the modem replies to any AT command.

Is this ok? Should it take the modem as long as 3 seconds to start responding to AT commands?
It seems like a great deal of time to leave a data connection waiting...

I appreciate your help.

Regards,
Agustin

 

[arunbharathi.arasu]

hi,You have to send 'A' 3 times before you send AT command

by sending 'A' three times SIM900 will wake up from sleep mode.

 

[aderregibus]

Thanks for your reply arunbharathi.

Where does it say that you need to send 'A' three times to wake from sleep?

Please note that the module is not in sleep mode, becuase I am setting AT+CSCLK=0, so I don't think that is the problem here.

 

[lilywei]

yes ACT ER14505 lithium battery