communication between 4 8051 with RS 485

[torana]

Hello,

My controller name AT89c51, I am trying to communicate between 4 micro controller with a distance with 150 meter. with RS 485 protocol.

for this i am using MAX 485 IC.

I have knowledge on RS232. I came to know that both RS232 And RS 485 Coding is same, But i am not conform whether BOTH RS232 and RS485 codes are same or not.

my code is not working on H/W. Bur same code is working with RS232 with PC. PLS help

PLS follow the H/W design.

 

[akhil_mohan]

check the termination resisitor...how will you identify the message for different protocol...

 

[torana]

thanking you,

Actually i am very new to this communication, i just refer this Circuit from net. it mention that 120 Ohm should be connected between two lines, And both should be Twisted, Thank you, Pls give me some guidance for making the code. thank you sir.

 

[akhil_mohan]

actually maxim ic take care of your conversion form 232 to 485... in code what you have to do is make a protocol(use stnadard) lik startbit,device id,read/write,data,checksum etc... so that you can communicate with microconteroller effectively....check for shorter distances then go for longer .........

 

[torana]

sir,

RS 232 having start bit, 8bit data and then stop bit, so how to give device address...... thank you

 

[akhil_mohan]

ok fine.... here you have to make frames ...tell me when you transmit something how will you identify which controller to receive... for that only make a frame format ... start means staring of a frame ..eg 2x,deviceid,read/write,address,data..2y,checksum .... for connection set up search in same forum...termination resistor is ok 120ohm...

 

[ABH]

try with lower boud rate.