How can I connect more than 1 RS232 device to a single micro?

Jul 28, 2003 7 Replies
F

Hi all,



I'd like to connect more than one RS232-device to the one RS232 being free on my SBC.



If I used RS485 I had to use a special prototcol, which besides the data containes the address of the slave device the master wants to speak to. No problem on the master's side. But those devices are completely unaware of anything other than one master connected to them. And as it is not possible for me to change the software of those devices (to tell them to listen to an address byte coming over a RS485 network), this solution seems to be ruled out.



At

formatting link
I found switchers being advertised, doing exactly what I need. But guess what, they are built to be used with PCs: Large boxes, heavy and - expensive. Nothing for my mobile robot.



There are ICs like the DS3695A from National Semiconductor, the MAX485 from MAXIM etc. They all have pins to enable/disable their lines. But if I understand it right these pins have to be set by the device hosting the chip. Or could my master enable/disable the DS3695A of a slave thus selecting it for communication? I guess, not.



Could I use a mux (or is it a demux?). Such ICs are used to get more I/Os than are actually available. Probably not the right thing for this job, I don't know. If it was that easy, the Internet wouldn't offer such large and heavy boxes.



Any hints? Any pointer is appreciated.



Many thanks and kind regards Franz GEIGER


Vote
Twitter Facebook LinkedIn
R

Hi

If you use XON XOFF handshaking then you only need switch TX and RX, how about a toggle switch or a relay even?

best regards

Robin G Hewitt

Vote
Twitter Facebook LinkedIn
G

Diode OR all the Tx outputs together into your Computor Rx line and use a pullup resistor. You have to do the networking software to address each unit so they talk politely only when polled by the master.

Vote
Twitter Facebook LinkedIn
P

No, he couldn't change the protocol he wrote.

If you only got one serial port and nothing else the only thing you can do is put a simple processor in the serial lines. These could respond to special commands and switch the serial lines for you.

Good luck,

Peter

Vote
Twitter Facebook LinkedIn
F

Hi Peter,

thanks for your response.

Can you (or anyone here in this group) recommend one to me? Seems it should have at least 4 RS232: Host, device 1, device 2, programmer. I'd really prefer an MCU ready to use with *very* few external electronics (I'm a "softie"), like all those stamps etc. (but in difference to those with more serial lines). Outsider recommended an SX, which I'm not familiar with (yet).

Kind regards Franz GEIGER

P.S.: Thanks, of course, to all other posters too!

"Peter van der Vos" schrieb im Newsbeitrag news: snipped-for-privacy@kitt.nl...

Vote
Twitter Facebook LinkedIn

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required