Monitoring RS485

Connecting nodes in parallel - yes, this is what RS485 is designed for.

If you want to connect a PC via RS-232 then you need to convert RS485 signal levels to RS232. Since you only want to listen this is simple. Connect a MAX481 back-to-back with a MAX232, with the MAX481 configured to permanently recieve and the MAX481's recieve data pin connected directly to the MAX232 transmit data pin.

Yes, but if it is two way communication it may be difficult to figure out who is sending what.

--DF

Or get RS232/RS485 converters here:

I'm not affiliated with them in any way.

John

Yes. Had a 9600 baud setup that broke into gibberish after a few characters were sent down the line. Quick and cheap solution was to monitor the RS485 wires using the "+" "-" inputs of a LM393 comparitor. LM393 and its output resistor both powered from spare data pins on the PC's LPT1 port. Data at the LM393 output pin was sampled at variable rates upto 200kHz from a PowerBasic programme. Stored data block allowed a storage scope type display of the actual RS485 voltage transitions. Data decoding and fault finding at my leisure.

10 minutes to build the device and a hour to programme the software. Nowadays we are no longer allowed to do it this way. regards john

During my search for a commercial converter I found this one:

this is very cheaper but i'm not sure that is what i need. Some one can see this item or know what this item do? John do you have the schema of your solution? Are you sure that this solution work fine?

Thanks Daniele

I did exactly this by just plugging a multiport RS485 card into a PC and using the receives of two different ports to monitor the traffic in either direction. A quick-and-dirty VB application displayed the results. Still does, actually..... :-)

Ken