RS232 is probably one of the most used, easy to develop and easy to apply communication protocol. We generally encounter to this standard at the MCU applications. But it has some restrictions.
It allows us to use maximum 15 meters cable. Good wiring, low baud rates and less noisy mediums may allow us to exceed this limit a little more. The main problem here , when the distance increases, the noise at the common ground line also increases. Another issue, RS232 allows only two devices to communicate reciprocally. More than two devices can not communicate at this line and we need another solution for this situation
RS485 is the standard that solves this problems. The main difference is, RS485 transfers the data depending on the potential difference between the two communication wires. The polarity defines the logic state of the signal. You can transfer data up to 1220 meters far away and with a rate up to 10 Mbs. 32 devices can join the RS485 network.
While transferring the data, MAX232 converts the signal coming from the DB9 connector to TTL/CMOS level. Then MAX485 transfers the input signal coming from the MAX232 to the RS485 line as a voltage difference. While receiving the data, MAX485 detects the data at the RS485 line and transfers it to MAX232 then output can be taken from the DB9 connector.
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