Serial communication Port
The port is a communication protocol for general device on a computer. Most computers include two RS232-based serial ports.
The serial port also a common communication protocol for instrumentation equipment; many GPIB-compatible devices also have RS-232 ports. At the same time, the serial communication protocol can also be used to collect data from remote collection devices.
Serial communication have 3 wires: (1) ground wire, (2) launch, (3) receive. Because serial communication is asynchronous, the port can send data on one line and receive data on the other.
Common PLC basic interface
RS-232
RS-232 (ANSI / EIA-232 standard) is a serial connection standard on IBM-PC and compatible computers. Can be used for many purposes, such as connecting a mouse, printer or modem, and can also connect industrial instruments.
RS-232 is limited to point-to-point communication between the PC serial port and the device. RS-232 serial communication is up to 50 feet.
RS-485
RS-485 (EIA-485 standard) is improvement of RS-422, because it increases the number of devices, from 10 to 32, and defines the electrical characteristics at the maximum number of devices to ensure sufficient Signal voltage.
With the ability of multiple devices, a single RS-422 port can establish a device network. Excellent anti-noise and multi-device capabilities. When establishing a distributed device network connected to a PC, other data collection controllers, HMIs or other operations in industrial applications, the serial connection will choose RS-485.
RS-485 is a superset of RS-422, so all RS-422 devices can be controlled by RS-485. RS-485 can be used for serial traffic over 4,000 feet of wire.
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