RS-232 (Electronic Industries Association Recommended Standard #232) describes a method of connecting a computer to an instrument by way of a communication channel, most often a modem attached to a phone line. The RS-232 standard has been revised four times. The current revision is called RS-232-D and was approved on November 12, 1986. The basic communications model is shown in this figure:
The Basic Communications Model
Computers, devices, instruments, terminals, or peripherals are called Data Terminal Equipment (DTE) since they terminate each end of the communications path. Modems are called Data Communications Equipment (DCE) since they facilitate the communication across the communication channel. (In RS-232-D, the term Data Communications Equipment has been replaced with the term Data Circuit-terminating Equipment.) The RS-232 standard describes the interface between the DTE and the DCE. The interface is made using a 25 pin D shell connector. The female connector is associated with the DCE and an interface cable with a male connector is offered by the DTE. The standard optionally allows this cable to be detachable from the DTE, however, no connector type is specified. Only the connection at the DCE is specified by the standard!
