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RS485 is a two-wire protocol where 0’s and 1’s are differentiated by the difference in voltage between the two wires. Electrically, this means it c
RS485 is a two-wire protocol where 0’s and 1’s are differentiated by the difference in voltage between the two wires. Electrically, this means it can be used over long distances (ie, up to 4,000 feet). To use RS485 the processors that are talking each need to have their own internal clocks and each separately need to be told the speed at which they will send the bits and how many bits make up one letter. The processors also need to agree on a way to determine whose turn it is to talk and whose turn it is to listen. Modbus is a common choice, but there are many others.
I2C is also a two-wire protocol, but the 0’s and 1’s are based on the voltage of a single wire and the second wire works as the clock. This configuration does not lend itself to long wires; I2C is usually used between chips on the same circuit board. It’s theoretical limit is only about 1m, but, as you’ve seen when using the MPL directly, 3m can sometimes be managed.
