RS232 passive splitter

Hello all,

Could anyone help with the following simple problem?

I just need to connect 2 or 3 devices with rs232 interfaces to one rs232 gsm modem.

All the devices have different addresses.

I would like to build a kind of passive splitter, but I would need correspondent schematics.

Thanks in advance.

Regards

Use an AND gate to combine the inputs to the Receive Data Input on the modem. Take the Transmit data output and run it to each of the devices Receive Data input.

The devices will have to agree on who is allowed to talk, and they will have to deal with unsolicited input generated by requests from the other devices. RS-232 is really not set up for this kind of thing. You can't just do this in hardware and expect it to work with off the shelf devices.

Hence something RS485 is good at but RS232 is point to point.

I have split RS232 signals but for a common device which didn't send any info. These wre overhead displays use for call ques and 2 or three needed to show the same info, most now come with a pass thru but this was a long time ago.

The reason an AND gate works for for combining other transmitters for your receiver can be seen from the DeMorgan equivalent. In the case of three inputs you have "a low OR a low OR a low is a low" With all three tansmitters idle the output is high. If two people talk at the same time you get hash. C'est la vie n'est pas?