To connect devices via RS-232, a multi-wire cable must be used. It is important to distinguish between those standards that describe the connectors or physical interfaces that are used to connect appropriate cables to a computer's physical ports, and standards that describe the electrical characteristics, or transmission protocols used Īlso referred to as signaling. Figure 1: RS-232 25-pin and 9-pin pinout diagrams. The RS-232 standard defines voltages of between +5 and +15 volts DC on a given pin to represent a logical zero, otherwise known as a space, and voltages of between -5 and -15 volts DC to represent the logical ones, otherwise known as a mark. RS-232 uses electrical signals to transmit the ones and zeros of the digital datastream. Supports speeds up to 115 Kbps using 16550 family UARTS. In reality, depending on the type of media being used and the amount of external interference present - RS-232 can be transmitted at higher speeds and/or over greater distances. RS-232 is officially limited to 20 Kbps for a maximum distance of 50 feet. Prevalence of RS-232 in the PC marketplace is so great that the term serial port has come to mean an RS-232 serial connection. Standardized by the Electronics Industry Association (EIA), RS-232 is currently in its third release (RS-232-C). The RS-232 protocol is currently the most commonly used serial standard for modem communication. There are several different serial communication standards available for use in modern day computers, including RS-232, USB, and IEEE 1394 (Firewire). Serial transmission is the basis of most data communication between computingĭevices peer-to-peer, or computing device and peripheral device such asĪ printer. The connections can be used to connect a computer to peripheral devices such as modems, scanners, PDAs, and so on, or as the basis for a directly connected computer-to-computer data connection. The most basic data communication technologies are those used to directly connect two devices. Point-to-Point Data Transmission Technologies These specifications are sometimes referred to as layer 0. The Physical layer does not define the specifications for media and connectors. There is no data recognition at the Physical layer only streams of bits. The first layer of the OSI Network Reference Model, the Physical layer, is responsible for the establishment, maintenance, and termination of the physical connections between communicating devices.
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