Comparison of RS-485 and RS-232C protocols

There are also many interface protocols, which can be found from some different connection lines on our computers. Now let's compare some of the differences between the RS-232C protocol and the RS-485 protocol. First, we will intuitively compare them from outside.
 
The theoretical transmission distance of RS-232C protocol is 13 meters ｡

The theoretical transmission distance of RS-485 protocol is 1200 meters ｡

What is a RS-485 interface? What is its characteristic compared to RS-232C protocol interface?

Because the interface standard of RS-232C Protocol appears earlier, it is inevitable that there are deficiencies, mainly has the following four points:

(1) The signal level of the interface is high, which is easy to damage the chip of the interface circuit. Because it is not compatible with the TTL level, the level conversion circuit must be used to connect to the TTL circuit ｡

(2) low transmission rate. During asynchronous transmission, the baud rate is 20 kbps ｡

(3) The interface uses a signal line and a signal return line to form a co-location transmission mode. This co-location transmission is prone to common-mode interference, so the anti-noise capability is weak ｡

(4) The transmission distance is limited. The maximum transmission distance is 50 feet. In fact, it can only be used about 50 meters ｡

For the lack of RS-232C, so there are some new interface standards, RS-485 is one of them, it has the following characteristics:

1. electrical Characteristics of RS-485: The logic "1" is expressed by the voltage difference between two wires as + (2-6) V; the logic "0" is represented by the voltage difference between two wires-(2-6) V. The interface signal level is lower than the RS-232C protocol, it is not easy to damage the interface circuit chip, this level is compatible with the TTL level and can be easily connected to the TTL circuit ｡

2. The highest data transmission rate of the RS-485 is 10 Mbps

3. RS-485 interface is a combination of balanced drive and differential receiver, enhanced common mode dry performance,
That is, the anti-noise capability is good ｡

4. the maximum transmission distance of the RS-485 interface is 4000 feet, in fact up to 3000 meters, and the RS-232C protocol interface is allowed to connect only one transceiver on the bus, that is, single-site capability. The RS-485 interface on the bus is allowed to connect up to 128 transceiver. It has multi-site capability so that users can easily build a device network with a single RS-485 interface ｡

Because the RS-485 interface has good anti-noise ratio, long transmission distance and multi-station ability, the above advantages make it the first choice of serial interface, generally only two connections, so RS485 interface are shielded twisted pair wire transmission. RS485 interface connector using DB-9 9-core plug-in seat, and intelligent terminal RS485 interface using DB-9 (hole ), the keyboard interface with the keyboard is RS485 using a DB-9 (needle ).