RS232 is the standard most widely used for interfacing peripherals to PC’s and is designed for serial communications with single instrument up to distances of 15 metres, in a low electrical noise environment. Connection is via a screened two core cable where the voltage signal on each line is referenced to the screen which is grounded.
RS232 only defines the physical layer electrical specification, not the protocol that is transmitted across it. Various protocols are possible including simple ASCII communications and Modbus RTU.
Many modern PC’s do not have RS232 ports, but USB to RS232 converters are available for use with computers that lack this type of port, as are convertors for USB to RS485 and RS232 to RS485.