This Standard specifies the quality of serial binary data signals employing startstop (Le., asynchronous) format at a data terminal equipment interface. The scope of this standard is limited to signals as defined in TIA Standards TINEIA-422-B Electrical Characteristics of Balanced Voltage Digital Interface Circuits, TINEIA-423-B Electrical Characteristics of Unbalanced Voltage Digital Interface Circuits, EIA-485 Standard for Electrical Characteristics of Generators and Receivers for Use in Balanced Digital Multipoint Systems, ElMIA-562 Electrical Characteristics for An Unbalanced Digital Interface and the electrical characteristic portion of EICVTIA-232-E Interface Between Data Terminal Equipment and Data Communication Equipment Employing Serial Binary Data Interchange.

For a signal quality standard at the interface with synchronous data circuit terminating equipment, see TIA Standard EIA-334-A, Signal Quality at Interface Between Data Terminal Equipment and Synchronous Data Circuit-Terminating Equipment for Serial Data Transmission

This Standard recognizes the need to have a number of different sets of standard performance requirements because of differing operating conditions that lead to a different way of implementing equipment. A number of performance characteristics, therefore, are defined for transmitting equipment and for receiving equipment, it being the intent that any receiving category may be specified to operate with any transmitting category, the actual selection being dependent on such factors as channel performance, acceptable error rate, and the economic considerations of the system.

Categories I and B, as defined herein, are specified for general purpose applications and the use thereof shall be assumed unless a different category is specified for the equipment used.

This Standard is of particular importance when the equipment in a system is furnished by different organizations. It does not attempt to indicate what action, if any, is to be taken if the limits are not met, but it is intended to provide a basis for agreement between parties involved.

Any equipment which is represented as complying with limits established by this Standard shall meet the applicable specifications with the ranges of those factors which are described as appropriate for the operation of the equipment, such as primary power voltage and frequency, ambient temperature and humidity. 

This Standard does not describe signal quality performance characteristics of data circuit-terminating equipment or the communications channel associated with it. Neither does it describe any requirement for error performance of the system or any of its components. Compliance of the terminais with the requirements for a particular standard signal quality performance category should not be construed as establishing an acceptable error rate for the terminals or the system.