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I am using atmega 2560 and SIM808. When I send an AT command to SIM808 it returns correctly. But sometimes I have seen that SIM808 returns the same AT command. Sometimes it occurs due to lack of power in SIM808 and due to Serial problem. But another time I have seen that, power and Serial are ok but it returns the same AT command. Why this type of problem occurs ?

  • What do you mean "returns the same at command"? – Majenko Sep 24 '18 at 6:10
  • Like that I sent "AT" normally it returns "OK" But sometimes I have seen that I send "AT" it returns "AT" – Iqbal Hossain Sep 24 '18 at 7:16
  • Unless you turn off echo it will always return AT\nOK\n – Majenko Sep 24 '18 at 7:18
  • echo has already turned off – Iqbal Hossain Sep 24 '18 at 10:31
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My default modems usually echo back whatever you send. So if you send AT it will first respond with AT followed by the OK response:

>> AT
<< AT
<< OK

Echoing can be turned off with the command ATE0 and turned back on with ATE1:

>> ATE0
<< ATE0
<< OK
>> AT
<< OK
>> ATE1
<< OK
>> AT
<< AT
<< OK
  • I have already followed these. After these commands I have used "AT+SHUT" it returns multiple times "AT+SHUT" – Iqbal Hossain Sep 24 '18 at 9:10
  • Are you sure it's the modem returning that data and not your code being broken? – Majenko Sep 24 '18 at 9:20

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