Telit GM862 problem [URGENT]

[johnny_hush]

MODERATOR ACTION: next time you flooded the board with same topic you will ban asking in one forum for same topic enough


I'm trying to test gm862 gsm modem by connecting it to PC, but it simply isn't working/responding.

I've connected TxD and RxD to MAX232N and I've used two zener diodes due to gm862's voltage levels. And after I've hooked up the hardware I've sent certain AT commands, but I don't ANY response.

So, in order to determine what is the problem I've disconnected everything form gm862 except for power supply and saw that when I turn on the modem, TxD pin (pin37) goes 'high' for a second or less and then it goes back to 'low', although it should always be 'high' when the TxD line is idle.

What the problem could be? Please help ASAP.
Thanks,
johnny

 

[blueroomelectronics]

Why is it urgent?

 

[johnny_hush]

Because I need to resolve this issue as soon as possible.

If you don't have any smart suggestions please don't go offtopic.

 

[blueroomelectronics]

Well the topic said [URGENT] with lots of capitals too. So I'm hardly off topic.

 

[blueroomelectronics]

It would probably help if you posted your source code and schematic. Else it's just guesswork.

 

[johnny_hush]

There is neither source code nor schematic.

The thing is simple: I connect only power supply, then I power on the modem and TxD pin is high only for a second, instead of being constantly high.

Can somebody help out? What can be a solution?

 

[blueroomelectronics]

If there's no schematic then what's with the MAX232 in post #1?
Maybe it need CTS/RTS or DTR/DSR handshaking.