What is the message format that can be used with RS 485 ?

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JoseNaveen

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i have implemented a uart for operating with a rs 232 port in my fpga. now i have to include another controller for operating with rs 485 . what is the message format that can be used with rs 485 .? is it the same as in rs 232 ..? i use a start bit,8 data bits, and a stop bit in rs 232..?
 

Re: RS 485 in FPGA

RS-485 is just a physical layer defined to be a multidrop network with diferetinal pair and thats it. Most tranceivers have direct interface to standard UARTs. You could use the same controler of the RS-232. But if you are using a multidrop network you must define some addressing protocol. Most networks make use of 9-bits serial with automatic address detection. But as i wrote before, you could make any kind of comunication over RS-485 as the tranceivers does not have any kind of specific package format, frame or protocol.
 
Re: RS 485 in FPGA

I would be reasonable, to include an automatic RS485 transmitter enable generation with the UART.
 
Re: RS 485 in FPGA

thank u for ur replies..thats what exactly i was looking for..
 

Re: RS 485 in FPGA

9-bit means u say that i can use 1 bit to notify that its a address byte so that a node in a multidrop network can be selected?
 

Re: RS 485 in FPGA

Yea exactly that. But you don't need to do that. You can just creat yourself a protocol to do that. But most of UARTS will work with 9-bits auto addressing.
 

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