This is in contrast to the half-duplex mode, when one link is used to receive and transmit data, which imposes a restriction on simultaneous operation, so in a half-duplex mode at one time, either the reception or transmission of information is possible. The RS-232 interface operates in full-duplex mode, which allows you to send and receive information at the same time, because different lines are used for receiving and transmitting. At a minimum distance, the speed is usually 115.2 kbps, but there is hardware that supports speeds of up to 921.6 kbps. The speed of the RS-232 depends on the distance between the devices, usually at a distance of 15 meters the speed is 9600 bps. The RS-232 interface (TIA / EIA-232) is intended for the organization of data transfer between the transmitter or terminal (Data Terminal Equipment, DTE) and the receiver or communication equipment (Data Communications Equipment, DCE) in the point-to-point scheme. Information transmitted via RS-232, RS-422 and RS-485 interfaces is structured as a protocol, for example, the Modbus RTU protocol is widely used in the industry. You will learn more about this in the article. Typically, TxD, RxD and GND ground lines are used, the remaining lines are needed to control the data flow. * For the RS-232 interface, it is not necessary to use all contact lines. The table shows the main differences between RS-232, RS-422 and RS-485 interfaces.ģ2 (with repeaters larger, usually up to 256) The RS-422 and RS-485 interfaces are widely used in the industry for connecting various equipment.
Rs 232 voltage serial#
The RS-232 standard is better known as a normal computer COM port or serial port (although Ethernet, FireWire and USB can also be considered as a serial port). The RS-232, RS-422 and RS-485 designations refer to interfaces for digital data transmission. Some devices provide test voltages on their interface connectors for this purpose.The main differences between RS-232, RS-422 and RS-485 Where it is necessary to permanently set a control signal to a defined state, it must be connected to a voltage source that asserts the logic 1 or logic 0 level. Unused interface signals terminated to ground will have an undefined logic state. Balanced, differential, serial connections such as USB, RS-422 and RS-485 can tolerate larger ground voltage differences because of the differential signaling. If the two devices are far enough apart or on separate power systems, the local ground connections at either end of the cable will have differing voltages this difference will reduce the noise margin of the signals. Use of a common ground limits RS-232 to applications with relatively short cables. This may also cause a hazardous ground loop. These also protect the device's internal circuitry from short circuits or transients that may appear on the RS-232 interface, and provide sufficient current to comply with the slew rate requirements for data transmission.īecause both ends of the RS-232 circuit depend on the ground pin being zero volts, problems will occur when connecting machinery and computers where the voltage between the ground pin on one end, and the ground pin on the other is not zero.
Rs 232 voltage driver#
The slew rate, or how fast the signal changes between levels, is also controlled.īecause the voltage levels are higher than logic levels typically used by integrated circuits, special intervening driver circuits are required to translate logic levels.
Rs 232 voltage drivers#
RS-232 drivers and receivers must be able to withstand indefinite short circuit to ground or to any voltage level up to ☒5 volts. Some RS-232 driver chips have inbuilt circuitry to produce the required voltages from a 5 volt supply. The standard specifies a maximum open-circuit voltage of 25 volts: signal levels of ±5 V, ☑0 V, ☑2 V, and ☑5 V are all commonly seen depending on the voltages available to the line driver circuit. Examples of control lines include request to send (RTS), clear to send (CTS), data terminal ready (DTR), and data set ready (DSR). Control signals have the opposite polarity the asserted state is positive voltage and the inactive state is negative voltage. Logic zero is positive and the signal condition is termed spacing. For data transmission lines (TxD, RxD and their secondary channel equivalents) logic one is defined as a negative voltage, the signal condition is called marking. Data signals and control signals use opposite polarity to represent a "true" or logic 1 asserted state. Valid signals are either in the range of +3 to +15 volts (logic 0), or the range -3 to -15 volts (logic 1) the range between -3 to +3 volts is not a valid RS-232 level. The RS-232 standard defines the voltage levels that correspond to logical one and logical zero levels for the data transmission and the control signal lines.
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