Problem with MAX3232

HI All,

I am using a MAX3232 to interface my GSM modem with PC. I am using five signals, ie Tx,Rx,RTS,CTS and also GND.

The schematic is attached with this thread.

The problem is that, i am not getting any replay from the modem.

my boudrate is 115K and i have selected the flow control none!

I need only to use RTS and CTS along with Tx and Rx

Its is confirmed that modem is working well.

My question is that is it necessary to use DTR and DSR signal for RTS and CTS?

Can you help me out pls

I think your software should start at a low baud rate like 9600, then let the software negotiate higher speeds.

Thanks 4 the replay sir,

but when i checked with the modem suppliers, they are telling that i should use 115k baudrate.

But they are using MAX3238 instead of MAX3232. Will that make any difference!!!!! (probably not. isn't it???)

You might need to send a speed command to the Rx modem, so it is a good idea to start at a low baud rate and work your way up. This is assuming the modem uses V.standards. You should look into what V.standard your GSM device uses, that should tell you what default modem speed to use.

P.S You don't need to call me sir. I work for a living

Here's the thing.
When modems first try to link up, the modems do not know what speed to use. Modem A speed? -----> Modem B speed?, so they usually default to slowest speed, which depends on standard. The software then negotiates higher speeds.

I use GSM modems for my work and I never use anything other than Rx and Tx.

I have also found that the Telit modules work out the baud rate instantly. However, I have only used them in the 1200 - 4800 baud range.