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.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |