communication protocol
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Hi, can any one tell me about the implementation of RS-485 and also about the difference btw full duplex and half duplex if example is provided it would be of great help thanks Uday
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Hi, can any one tell me about the implementation of RS-485 and also about the difference btw full duplex and half duplex if example is provided it would be of great help thanks Uday
I can tell you about the basics. RS-485 works by voltage differential. Their are two lines which are either +ve or -ve depending on whether a 1 or a 0 is being transmitted. These lines are labelled A and B. So a 0 = A+, B- a 1 = A-, B+ (or visa-versa) Also, many devices can be on an RS-485 bus at a time. They need to use some kind of communication protocol to decide when they want to transmit on the bus. Any number of devices can listen, but only 1 can transmit at a time or you get garbled communication. Typiclly, you have 1 master device which initiates all transmissions, and then the other devices reply to the message, but they have to do so in a set time frame. DOnt forget to use checksums etc if needed to avoid bad messages. Full-duplex/Half duplex. In one of these modes you also receive in your input buffer what you send, in the other you do not. I forget which way round it is. Hope this info helps. Roger Allen Sonork 100.10016 If I had a quote, it would be a very good one.
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I can tell you about the basics. RS-485 works by voltage differential. Their are two lines which are either +ve or -ve depending on whether a 1 or a 0 is being transmitted. These lines are labelled A and B. So a 0 = A+, B- a 1 = A-, B+ (or visa-versa) Also, many devices can be on an RS-485 bus at a time. They need to use some kind of communication protocol to decide when they want to transmit on the bus. Any number of devices can listen, but only 1 can transmit at a time or you get garbled communication. Typiclly, you have 1 master device which initiates all transmissions, and then the other devices reply to the message, but they have to do so in a set time frame. DOnt forget to use checksums etc if needed to avoid bad messages. Full-duplex/Half duplex. In one of these modes you also receive in your input buffer what you send, in the other you do not. I forget which way round it is. Hope this info helps. Roger Allen Sonork 100.10016 If I had a quote, it would be a very good one.
Roger Allen wrote: Full-duplex/Half duplex. In one of these modes you also receive in your input buffer what you send, in the other you do not. I forget which way round it is. Are you not getting confused with "loop back"? Full-duplex means that both transmission and reception of data can occur simultaneously. Half-duplex means that only transmission or reception can take place at any one time. There is also a form of communication called Simplex which means that only transmission or reception ever occur. Free
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Roger Allen wrote: Full-duplex/Half duplex. In one of these modes you also receive in your input buffer what you send, in the other you do not. I forget which way round it is. Are you not getting confused with "loop back"? Full-duplex means that both transmission and reception of data can occur simultaneously. Half-duplex means that only transmission or reception can take place at any one time. There is also a form of communication called Simplex which means that only transmission or reception ever occur. Free
FreeLancer wrote: Are you not getting confused with "loop back"? Hmmm, maybe. I am going by the driver stuff installed for the RS-485 card in my PC. It can have a half/full duplex mode. Your probably right. Its been a long time since I looked at it*. * Need to get my memory chips upgraded - finally I may have 2K! Roger Allen Sonork 100.10016 If I had a quote, it would be a very good one.