PU/PD resistors are usually required in RS485 networks to set a defined idle state when both transmitters are disabled. They are specified in many RS-485 based IO-standards, e.g. PROFIBUS.
Yes I know the purpose of PU/PD resistor, but what I was asking is that do I need to add PU/PD resistor on Slave node also? (as Mention in my circuit diagram)
I don't know what "stopped working" exactly means.
Stopped means that during working slave stop to reply the master,then when I replace the IC it start to replay again.
This behaviour is very random,sometime it occur with in a hour and sometime it occur after months.
I have operated RS-485 multi-drop networks at 19200 Baud with > 1000 m cable length, by the way.
That's really good, then you have a very good idea about RS-485 networks
I have some concerns in my circuits
1. Transil Protection missing : I think I should use CDS0T23-SM712 TVS diode
2. Biasing resistor needs to be removed from slave side
3. The RS-485 specification recommends connecting a 100-W resistor of at least 0.5 W in series between each node’s signal ground and the network’s ground wire, as attached Figure shows. This way, if the ground potentials of two nodes vary, the resistors limit the
current in the ground wire.
https://obrazki.elektroda.pl/index.php
4- May be we can remove the termination resistor from circuit. I decided to remove the termination resistor after doing this calcultaion
Propagation velocity = 0.66 x speed of light = 197863022.28 m/s.
For a 30m cable the propagation delay should be 455 ns assuming it damps out in 3 round trip.
Baud rate is 9600,so bit width will be 104.17 us .
Since propagation time is short relative to the data bit duration, the effect on the signal quality is minimized, and I don't need any termination.
Kindly do comment on my calculation and assumption, and give your valuable advice
Thanks in Advance..