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Interfacing GSM Modem

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Hi , Im trying to interface T290i erricsson to a microcontroller , i've the datacable , AT commands works fine in hyperterminal , but i get rubbish charachters when i interface it to the uC and display the results on the LCD , i've used the free serial port monitor , and i've seen that RTS and DTR are green ( blinked) , and the datacable is connected to the uC RS232 which is a two transistors level shifters , i dont know where to connect RTS and DTR ?
I didnt understand , what do you mean by my uC can keep the data ?

By the way, i found that when i connect the cell to the PC , and use hyperterminal , the mobile gets charged , that never happens when i connect the cell to the uC .


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Blueroom had checked up what sort of phone it is. I had wrongly assumed that you would be able to use RS232.

USB is a lot more difficult to connect to a microcontroller.

What I meant by

If your uC can keep up with the data from the 'phone
was about the speed of the data arriving from the phone. On an RS232 link, data will arrive and has to be processed by the microcontroller. If the microcontroller can't process the data as fast as it arrives, then the DTR or RTS lines can be used to pause the data.

It is usually quite easy for the microcontroller to process the data as fast as it can arrive so there is never any need to pause the data.

This is not about Baud rate. If the data is sent at 9600 baud, then a bit will take 104.2 µs and a byte (8 bits plus start and stop bits) will take 1042 µs. Anything receiving a byte has to be able to receive at that speed, but there may need to a pause between the next byte.
This phone isn a usb one , it has a datacable which can be connected to the serial port of the PC .
is this connection correct ??

Mobile-->datacable -->DB9 <--DB9 of uC <-- two transistor level shifters <-- tx,rx of uC
Yes, but the cell when its connected to the DB9 of the uC it doesnt get charged even if when i send AT\r\n to it , it should start charging .. i feel that i should connec DTS,RTS to somethings ... connect them to VCC ??
blueroom , the datacable is Eri T68 and it works fine with the hyperterminal

by the way i've connected DTR,RTS to 5V and i can now do AT commands with my uC , i can send SMSs to the cell from the uC .


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Perhaps it's a version with a DB9 but I can't find any reference to that type.

Well since you're using a 16F84A you can invert your serial data and connect directly to the RS232 pins with a 22K resistor on your PICs RX and the TX out directly.

Heres a 2 transistor version similar to the one I used on my Firefly kit.


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I can't imagine any cellphone using RS-232, but who knows...
it doesnt like it , because at DB9 of the uC the RTS ,DTS left open , got it ??
but the question why they need to be tied to 5V ?!!
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