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Problem with sending AT commands through 8051 (T68i and AT89S52)

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Re: T68i and AT89S52

Finally, the phone manages to send SMS.

Thanks alot for your help!

I connected pin7 to 5V and pin 8 to ground, and everything works properly.

Just one more question for curiosity. Is it really possible to built an SMS controller using only TX, RX and GND? Or it is only an exceptional case for the model T68i?
 

Re: T68i and AT89S52

Hi,
Wov, Hearty congrats. By the way, pin 8 is output of a Max gate, just leave it free, do not ground.

And regarding SMS application, only TX/RX and ground is sufficient, some other phones are (mis)using DTR/RTS signals just to power the cable circuits and they do not need an external 5V connection as in 68i.

Regards,
Laktronics
 

Re: T68i and AT89S52

Hi,
Thanks for your thanks. By the way I forgot to tell you that you also have unused gates of a Max 232 on your 8051 board. You can use the unused TX driver to generate the RTS signal at pin7 of your 8051 connector instead of connecting a 5V to it. You ground the input pin of this TX gate so that at pin7 you get the positive RS232 level. Leave pin 8 on the 8051 side connector open. The input of the unused RX gate of the IC may be pulledup to Vcc through a 470 ohm resistor. This will also ensure that the inputs of the unused gates are not left open.

Regards,
Laktronics
 

T68i and AT89S52

Thx for your suggestion, I'll try this
 

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