GSM modem not working with PIC! Both modem & PIC work fine with PC

[financecatalyst]

Although I am sure it works on PC with just TX, RX nd Gnd, have tried to connect to PC just with these 3 wires?

I tried it now, I could not type in my hyperterminal anymore as soon as I connected my modem to the PC with only 3 wires. As soon as I connected 9 pin serial cable, everything starts working fine.

Also are you sure about 4800 baud?

Yes, baud rate is 4800.

[aratti]

I tried it now, I could not type in my hyperterminal anymore as soon as I connected my modem to the PC with only 3 wires. As soon as I connected 9 pin serial cable, everything starts working fine.

Was hyperterminal in hand shaking mode?

See the modem manual, if the modem is in handshaking mode by default, in such a case you have to set it for no flux controll.

Al.

[financecatalyst]

Was hyperterminal in hand shaking mode?

See the modem manual, if the modem is in handshaking mode by default, in such a case you have to set it for no flux controll.

Al.

I have not got the manual but I have opened the modem and saw that sim300 is the module which the modem is built on. I have checked sim300 datasheet but could not understand many things as I do not have too much of a technical background.

Can you advise me, what AT commands can do this job.
I also find this on the net - http://www.london-electronics.com/alpha_232_conns.gif
Is this an alternate way to go to solve this problem (RTC - CTS connected together & also pins 6,1,4 connected together? I do not want to try it unless it is safe to do so, only have 1 modem

Also, how can I find out if Hyperterminal is in Handshaking mode? One more thing I would like to mention here which I read from sim300 datasheet is that the modem supports and by default has Autobaud from 1200 to 19200.

[aratti]

Also, how can I find out if Hyperterminal is in Handshaking mode?

When you set the baud rate you can set also the flow mode. See the three snaps attached.

Al.

[financecatalyst]

When you set the baud rate you can set also the flow mode. See the three snaps attached.

Al.

No, the handshake mode is "None".

[falingtrea]

The setting of hyperterminal may not tell you whether the modem itself needs flow control . Typically if flow control is turned off, the RTS pin is set "high".

One thing you can try is either to set no flow contol on the SIM300(if you can), or wire an output RS232 buffer to pin 7 of the serial cable and pull the input low, which should make the RTS active on the SIM300.

[Kolesnikov]

This is a feature of the sim300 module. If you connect it via 3 wires then you have to connect its RTS with CTS - these are pins 7 and 8 on the DB9 RS232.