communication rs485

[maryem]

Hello, i need to use bus rs485 in half duplex multimaster multislave , this protocole is it existing ???
Can i use one adress to a group of slave or i will have problem if my master can't disting between them ??????
i need each master control a group of slave and a master that command all devices (slaves and masters )
how can implemented this??
Please there are someone can help ???

 

[be80be]

Google Modbus
read this https://www.embedded.com/design/connectivity/4023975/Serial-Protocols-Compared

 

[JimB]

Some years ago I did a project which used two computers and three PLCs.
The communication protocol was MODBUS, and the electrical connection was RS485.

The two computers were MODBUS Masters. In that system only one computer could be Master at any one time.
The two computers were connected in a dual redundant arrangement where one computer as "online" controlling the process, and the other was "standby" in case of failure of the online computer.
Whichever of the two computers was online, that computer communicated with the PLCs.
The three PLCs each had a unique MODBUS address. Addresses 1, 2, and 3 if I remember correctly.

JimB

 

[maryem]

OK ,
i find in
mikroC PRO for PIC Libraries
a RS-485 Library master slave : Can i use it in my protocole multimaster multislave ?,, But I don't understand how he sent the data :
dat[0] = 0xAA;
dat[1] = 0xF0;
dat[2] = 0x0F;
dat[4] = 0; // ensure that message received flag is 0
dat[5] = 0; // ensure that error flag is 0
dat[6] = 0;
i interstand that it use dat[4] and dat[5] to control the reception but what's the meannig when he is put this :
if (dat[4]) { // if message received successfully
cnt = 0;
dat[4] = 0; // clear message received flag


there someone can help please ??

 

[maryem]

OK ,
i find in
mikroC PRO for PIC Libraries
a RS-485 Library master slave : Can i use it in my protocole multimaster multislave ?,, But I don't understand how he sent the data :
dat[0] = 0xAA;
dat[1] = 0xF0;
dat[2] = 0x0F;
dat[4] = 0; // ensure that message received flag is 0
dat[5] = 0; // ensure that error flag is 0
dat[6] = 0;
i interstand that it use dat[4] and dat[5] to control the reception but what's the meannig when he is put this :
if (dat[4]) { // if message received successfully
cnt = 0;
dat[4] = 0; // clear message received flag


there someone can help please ??