tailieunhanh - RS-422 BALANCED VOLTAGE INTERFACE

Specifying compliance to RS-422 only establishes that the signal between the specified devices will be compatible. It does not indicate that the signal functions or operations between the two devices are compatible. | RS-422 BALANCED VOLTAGE INTERFACE Specifying compliance to RS-422 only establishes that the signal between the specified devices will be compatible. It does not indicate that the signal functions or operations between the two devices are compatible. The RS-422 standard only defines the characteristic requirements for the balanced line drivers and receivers. It does not specify one specific connector signal names or operations. RS-422 interfaces are typically used when the data rate or distance criteria cannot be met with RS-232. The RS-422 standard allows for operation of up to 10 receivers from a single transmitter. The standard does not define operations of multiple tristated transmitters on a link. The RS-422-A interfaces between the Data Terminal Equipment DTE and Data Communication Equipment DCE or in any point-to-point interconnection of signals between digital equipment. It employs the electrical characteristics of balanced-voltage digital interface circuits. The balanced voltage digital interface circuit will normally be utilized on data timing or control circuits where the data signalling rate is up to 10 Mbit s. While the balanced interface is intended for use at the higher data signalling rate it may in preference to the unbalanced interface circuit generally be required if any of the following conditions prevail The interconnecting cable is too long for effective unbalanced operation. The interconnecting cable is exposed to an extraneous noise source that may cause an unwanted voltage in excess of 1 volt measured differentially between the signal conductor and circuit common at the load end of the cable with a 50 ohm resistor substituted for the generator. It is necessary to minimize interference with other signals. Inversion of signals may be required . plus to minus MARK may be obtained by inverting the cable pair. Applications of the balanced voltage digital interface circuit are shown in Figure 1. DTE Data Terminal Equipment DCE Data .