IBM 5280 Distributed Data System - Index of

COMMUN ICATIONS CONTROLThe communications attachment consists of communications adapter, a communicationsdata trap, and the communications microprocessor. The communicationsmicroprocessor supports one communications line. The adapter can provide datalink support for BSC or SOLC protocol. The data trap is used by the communicationsmicroprocessor to store diagnostic information. See the Data Areas and DiagnosticAids Handbook and the Communications Utilities Reference Manual forinformation about communications.The communications microprocessor handles communications I/O, including sendingstatus information and data to the host, receiving data and status informationfrom the host, and blocking and deblocking records. The communications microprocessoruses a communications access method, which may be an IBM programproduct or a program written by the user, to control communications operations.The communications microprocessor interfaces with the communications accessmethod through the communications control block. The communications accessmethod, in turn, interfaces with the application program through the communicationslOB. The communications lOB is described by a control statement in thesource application program. The communications access method and communicationscontrol block must be loaded into a main storage partition. The applicationprogram and communications lOB are loaded into another main storage partition.Error Recovery and External StatusThe communications microprocessor attempts to recover from certain I/O errorsand records errors in an error recording table located within the communicationsaccess method partition. If the error or condition is not resolved by the communicationsmicroprocessor, the communications access method places a 4-digit conditioncode in the communications lOB and reports external status.5280 Functions and Storage Overview 23