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[uXing]

I am starting to do a simple mobile phone. And I have got a kit from your company, which is GM862-QUAD module and GM862 EVK V3 RS232 evalution board.
I do the connection as below.(between 89c52 and GM862 , I have just connect the TXD line)

So, I try to send out simple AT command through TXD(Pin 11) from MCU(89c51) to gm862 like this

void serial_init()
{
SCON=0X50; //mode 1 where REN=1,can ready to receive 1 START BIT, 8 DATA BIT, 1 STOP BIT
TMOD=0X20; //enable timer 1 to operate in 8-bit auto reload mode
TH1=0XF9; //set the baud rate to 9600
TR1=1; //turn on time 1
TI=1; //ready to transmit
}

void send(unsigned char s)
{
SBUF=s; //send out the character
while(!TI) //wait until sent
{
}
TI=0;
}

main()
{
serial_init();
//if button is pressed,do the following(answer the call) , I just skip the keypad part here
send('A');
send('T');
send('A');
send('\r'); //carriage return

}

So I dial to my GM862 , it is ringing. But when I press the button to receive the call. It doesn't any response (still ringing).
So what's wrong is it? Is there any hardware connection is wrong? Can I just connect TXD and the other(RXD,CTS,RTS) are all left disconnected?
Is the problem caused by the baudrate? The crystal I used in MCU is 12M , so i set the baudrate to 9600 by TH1 = 0XF9. But it seems that GM862 is autobauding, so I think it's doesn't matter.

Please help me, if this simple command is worked, I can do further things easily.

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