RS485 controlling querry

[assadmahmood]

Greetings EveryBody!
I have to interface multiple slaves with one Master, master can either be a microcontroller or a computer (PC), by using RS485 interface. Its my first attempt to interface something by RS485. I read about it and got the concept that how to interface MAX485 and data transfer in it etc.
Somethings are still unclear which I have to ask from you experts.

1- How to control RE and DE signals of MAX485 by microcontroller? and what to do with them?
2- If MAX485 is interfaced with PC via MAX232 then it is recommended to control RE and DE by RTS pin of Serial port. OKay, but how to control that, what to do in software's side?
3- If Master calls something, would it be listen by all the slaves?

Kindly let me know these thing bcz I have to do this task with in very short given time.

Many thanks for your kind consideration.

 

[barry]

Here's how it basically works:
1) All the slaves have their receivers turned on, and the transmitters off. (DE off, RE on)
2) The master turns on it's transmitter(DE on) and sends a message to a specific address, then turns off and turns on it's receiver.
3) The slave whose address was sent waits for the master transmitter to turn off("turn-around time"), and then turns its transmitter on and transmits a message to the master.
4) Slave turns it's transmitter off.
5) Repeat.

 

[assadmahmood]

Mr.Barry.
Many thanks for your knowledgeable post. The thing you told in the post is very easy with microcontroller, I got it now.
Now just suppose our computer is Master and we are sending and receiving messages through hyperterminal/docklight/hercules or any other serial port software then in such case how to control DE/RE pin?

 

[barry]

I'm not familiar with docklight or hercules, but hyperterminal will not (to my knowledge) control the RS-485 functions. You are also going to have to control the DE on all of the slaves. (I don't think there's an issue with keeping all the receivers enabled constantly.) I think you can purchase RS-485 boards that will plug into your PC, and the drivers provided with the board will control the RS-485 bus.

 

[assadmahmood]

Greeyins EveryBody!
If Master is PC (computer) and all slaves are microControllers then is it possible to interface MAX488 or MAX490 with MAX232 on the PC side while to interface MAX485 with all slave microControllers in the same bus?