Hello
Here is a famous circuit that I should work with it.(Ic=max485)

But I have some other works that I was faced with different problems
1) if I remove RT or select a high value , what is it's effects?
2)for some ICs with safe-fail features can we remove RT?
3)Actually I put RT=120 ohm and my two get hot, why?
4)it is normal that an IC cosume more than 50mA when I remove the other one(IC)?
5)I see in different projects that these ICs damage and we should change them ASAP , what reasons damage them?
6) If both of them use different power supplies( transformer or SMPS) , their activities doesn't change?
7)according to this link (http://www.chipkin.com/rs485-cables-why-you-need-3-wires-for-2-two-wire-rs485/) is it necessary to use ground wire? ( for 1.5m to 1km)? and for protecting if we want to use shield wire what should we do with this extra wire?


Thanks in advance and sorry to ask a lot questions

 

For long distances a earthed shield is recommended.
It is not necessary to couple the GND pin from one to the other.
Max.

 

1)I think when I don't use max45 between two line (A,B) I have 5V (if I bias max485 with 5V) so Iout=(5/120)=40mA so it consume 40mA without any connection with other ICs?
2)could you tell me what do we understand from these diagrams?

 

Thanks MaxHeadRoom for your explanation and comment.
But if we use ground wire we are face with ground loop effect and it shows it's effect more than little distance.Am I right?

 

A ground loop usually exists if both ends of the shield are earth grounded,
Max.

 

Your RS-485 setup is incomplete. Network lines A and B must be biased with a pull-up resistor on line A and a pull-down resistor on line B.

 

Thanks MaxHeadRoom and Mrchips for your comment

1)why do we need to use pull-up and pull-down resistor while it doesn't mention in datasheet? and how can we define their value?

 

Check out this on-line calculator:

http://alciro.org/tools/RS-485/RS485-resistor-termination-calculator.jsp

 

Thanks for your response and your helpful link
Could you introduce me good references about max485 that I get my all answers in post 1?

 

First stop is always Wikipedia:

https://en.wikipedia.org/wiki/RS-485

Here are a couple more references:

http://deltamotion.com/support/webh...and_Wiring/RS-485_Termination_and_Biasing.htm

https://www.maximintegrated.com/en/app-notes/index.mvp/id/763

 

Thanks for your response.
1)I want to know it is very important to use biasing network while our chip has internal fale-safe feature or internal biasing? as you see in attachment
2)for small length can we remove termination resistor or use one in slave or master ?

 

1)I think when I don't use max45 between two line (A,B) I have 5V (if I bias max485 with 5V) so Iout=(5/120)=40mA so it consume 40mA without any connection with other ICs?
2)could you tell me what do we understand from these diagrams?

I can not see the reply for this post.
Can any one may please explain this in details?
Mr. chips has added very helpful links.
Mr chips, MAX HEAD ROOm and Baby_2 Can you explain this threat.The about mentioned plots are confusing for me.
Thanks in advance..