1. RS-232-C is a serial physical interface standard developed by EIA (Electronic Industry Association). RS is an abbreviation of the English "recommendation standard", 232 is the identification number, and C is the number of revisions. The RS-232-C bus standard has 25 signal lines, including one main channel and one auxiliary channel.
In most cases, the main channel is mainly used. For general duplex communication, only a few signal lines are needed, such as one transmission line, one reception line, and one ground line.
The data transmission rate specified by the RS-232-C standard is 50, 75, 100, 150, 300, 600, 1200, 2400, 4800, 9600, 19200 baud per second.
According to the RS-232-C standard, the driver is allowed to have a capacitive load of 2500pF, and the communication distance will be limited by this capacitor. For example, when using a 150pF/m communication cable, the maximum communication distance is 15m; if the capacitance per meter is reduced The communication distance can be increased. Another reason for the short transmission distance is that RS-232 is a single-ended signal transmission, which has common ground noise and cannot suppress common mode interference. Therefore, it is generally used for communication within 20m.
2, RS-485
RS-485 bus, RS-485 serial bus is widely used when the communication distance is required to be several tens of meters to several kilometers.
RS-485 uses balanced transmit and differential receive, so it has the ability to reject common-mode interference. In addition to the high sensitivity of the bus transceiver, it can detect voltages as low as 200mV, so the transmitted signal can be recovered beyond the kilometer.
RS-485 uses a half-duplex mode of operation, and only one point can be sent at any time. Therefore, the transmitting circuit must be controlled by an enable signal.
RS-485 is very convenient for multi-point interconnection and can save many signal lines. Application RS-485
The distributed system can be networked, allowing up to 32 drives and 32 receivers to be connected in parallel.
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