How to build a network on RS-485???

Question

User interface

Hello.
With your permission, point by point.
1) There are 3 devices that need to be networked based on RS-485.
One device transmits data, two receive them, which switching device should be used??
2) In the second case, there are 4 devices between which two-way interaction is necessary (control, receive data, transfer), what will the switching look like in this case?
3) It is also not clear the condition for the presence of a transistor to maintain the wave resistance, for data transmission. Is the transistor mounted in the equipment by the manufacturer or in the cable, or does it need to be integrated into the network circuit during construction ????
4) and more, it is not unimportant whether it is necessary to configure the device somehow, to set addresses??

Answer 1

The topology in RS-485 is a bus. All devices are connected in parallel on one cable. See specifications for the cable in the documentation for the device.

Answer 2

1) RS-485 - bus. hang everything on one cable. However, if this is a modbus, then the scheme of 2 masters and one slave via rs-485 will not work.
2) RS-485 - bus. hang everything on one cable.
3) it is not needed for short distances. Generally placed at the end of the line.
enough twisted pair. 1 pair for + and - from the second pair take one wire as "common"
www.softelectro.ru/rs485.html
www.bookasutp.ru/Chapter2_3.aspx
4) It depends on the protocol.
Give data: what kind of devices, what protocol.
In general, there are specialized forums - they will help: asutpforum.ru/viewforum.php?f=12

Answer 3

1) Hang devices on the same bus, give them ID addresses, if you don’t want to use existing industrial protocols (for example, Modbus-RTU or ProfiBUS) or they don’t suit you for some reason, come up with your own rake. Further in the rake you encode commands. (for example: if we send 0x01, then we are preparing the transfer of the configuration, 0x02 - we are transferring the configuration, 0x03 - polling the device status, 0x04 - setting the value of the "such and such" parameter, etc.) We encode the master and slave and here you are.
2) Everything is exactly the same, but specify a different mode in the config. For example TokenRing can be used if the master/slave is not suitable for the job.
3) It depends on the length of the bus and interference. You need to read the spec at 485.
4) All devices that I have coded had such parameters. I’ll even say more, the device’s configuration was uploaded to the flash, in which there was everything, starting from the input / output settings, port numbers, the logic of the peripherals, the values ​​​​of the polling times and the operating mode of the device itself. After the start, this config was read, checked for acceptable values, the device was configured, self-tested and put into operation. In any emergency, a failed device could be replaced with a known working one, and for this it was simply necessary to plug the connectors, drain the accumulated information, upload the configuration to the new device and assign it the address-ID of the faulty one.

Answer 4

Is RS-485 mandatory? Look at CAN.
electronix.ru/forum/index.php?s=&showtopic=108475&...