3-wire rs232

[Willirb1]

I hope someone can help. I have a vending machine with a control board to which, according to the manufacturer, one can connect a GSM modem. My problem is that it only has GRD, TXD and RXD. How is it possible for this setup to work without the other modem signals, RTS, CTS, DTR, DSR,CD and RI.

 

[werner]

this is pretty common...just make sure the interface board uses proper rs232 signals, and not ttl, in which case you would need to use a max232 or a max233 to interface to it first (some of the older nokia cellphones had a similar arrangement...a 3 wire serial interface, but at ttl levels...so the "nokia data cables" were nothing more than a max232 type interface hooked up to the phone)

something like this http://www.seattlerobotics.org/encoder/aug97/cable.html

always check first if it is ttl or rs232, else you could blow things up

 

[mancombseepgood]

Tx->Rx, Rx->Tx, Gnd->Gnd

I hope someone can help. I have a vending machine with a control board to which, according to the manufacturer, one can connect a GSM modem. My problem is that it only has GRD, TXD and RXD. How is it possible for this setup to work without the other modem signals, RTS, CTS, DTR, DSR,CD and RI.

...
Last time I hooked something like that up was using null modem cable to leased line modem setup (modem handles handshake and connection - no dialing) and connection is via null modem cable to PC.

 

[Willirb1]

If it is true RS232 signals from the board, I'm still left with only the three signals(wires), what then???

 

[mancombseepgood]

Well, I can't really comment other than to say that a GSM modem must surely be different to standard analog. Why can't they support you?