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SIM 300 Modem problem communicating with uC but works well with PC

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alokdaga

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I am trying to use SIM300 GSM Modem with 16f877. When I connect it to PC, it works ONLY when the flow control is set to XON/XOFF in the com port setting. It works well with hyperterminal. When I connect it to uC, it just does not communicate.

On the other hand I have a wavecom Modem, which works with PC when the flow control is set to HARDWARE. When I connect this to uC, it works absolutely fine.

Can anybody guide me on this? In case the code and schematic had problems, the setup would not have worked with the wavecom modem.
 

You "NONE" setting I have tried both modems works with that setting..
No flow control at all..
 

The problem is when I try communicating with PIC ... Works well with Wavecom modem but not with SIM 300 Modem....
 

do you use the same cable to test wavecom and SIM300 modems. if yes then SIM 300 will not work with wavecom serial cable as the tx and rx are interchanged. so use another cable and swap tx and rx at one end of cable.
 

ckshivaram said:
do you use the same cable to test wavecom and SIM300 modems. if yes then SIM 300 will not work with wavecom serial cable as the tx and rx are interchanged. so use another cable and swap tx and rx at one end of cable.
Click to expand...

But with the same cable if I just change the setting of flow control, it works.... whereas with uC - it does not work !!!
 

you should not change the hyperterminal settings for modems, it should work with hyperterminal with no flow control. check if sim300 works with flow control as none on interchanging the tx and rx pins.
 

interchanging pins do not help ! my code in picbasic is simple.. this code is working with wavecom.. and sim300 modem is working with PC on XON/XOFF...

SEROUT portb.0, N9600, ["AT+CMGS=","xxxxxxxxxx",10]
PAUSE 500
SEROUT portb.0, N9600, [#CD1,CD2,CD3,26,10]
SEROUT portb.0, N9600, [10]
LOOP: GOTO LOOP
 

wavecom modems are designed to take carriage return and line feed as terminating the character, but SIMCOM modems use \n \r and some modems take ctrl+z and some take only \r. so it depends on the modem which we use. this is documented in the application note of the modem.
 
In my view in in case of uc ( micro-controller) there are couple of possiblities....check baud rate....assign every thing as char[] s1 ="AT +" commands and then try out...some time ASCII value conversion is required ...check the command senquence on hyper terminal or tera term on PC and uc communication....will help to solve the problem....

good luck
 

Any idea about SIM300 termination ? Will try and see the documentation.

ckshivaram said:
wavecom modems are designed to take carriage return and line feed as terminating the character, but SIMCOM modems use \n \r and some modems take ctrl+z and some take only \r. so it depends on the modem which we use. this is documented in the application note of the modem.
Click to expand...
 

Terminations in sim300
control z that is 0x1A is used to terminate sms
and \n\r is used to at commands
 
Tried with \n \r i.e. 10 and 13 both... did not work :(
 

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