IBM 5280 Distributed Data System - Index of

1Partition lOBTIle partition lOB describes the partition and the program loaded into the partition.The main microprocessor loads this information into the fields of the lOB, usinginformation from the common area and from the application program. During programexecution, the main microprocessor uses the information to determine thepartition status, the program status, the address of the next executable instruction,and how long to execute instructions within the partition before going to the nextpartition.The absolute address of the beginning of the partition is stored in the lOB. Themain microprocessor adds this address to the reiative addresses stored in the partitionto generate absolute addresses for the program instructions.A timer is set when the main microprocessor enters a partition. The lOB specifieshow long the main microprocessor executes instructions within the partition. Thistime is determined by the application program. The main microprocessor exits thepartition when the time limit is reached or when it encounters a nonoverlapped I/Oinstruction that is to be handled by a device microprocessor.Logical I/O TableThe logical I/O table consists of one 4-byte entry for each lOB that is used in theprogram. Each entry contains the address of the lOB, flags, and other i1lformationdescribing the lOB. The entries are numbered sequentially from hex 00 to 15,corresponding to the numbers assigned to the lOBs. The keyboard/display isalways entry zero. When the main microprocessor encounters an I/O instructionduring program execution, the instruction specifies the number assigned to the lOBthat describes the work. The main microprocessor uses this number as an index intothe logical I/O table; the entry at this index contains the address of the lOB andspecifies the I/O device that is to perform the work.Keyboard/Display lOBEvery application program must have a properly initialized keyboard/display lOB.The keyboard/display lOB contains information to control all I/O via the keyboard/display to which the partition is assigned. This information includes the address ofthe I/O buffer, the address of the object code that controls the format of the recordson the screen and in the I/O buffer, and the address of control tables located in keyboard/displaystorage. Keyboard display storage is not part of main storage; it islocated within the keyboard/display attachment. The keyboard/display storagecontains translate tables and other control information used by the keyboard/displaymicroprocessor to process keystrokes and to display characters on the screen.Registers and IndicatorsImmediately following the partition control area are bytes that can be used forindicators, binary registers, and decimal registers. The first 32 bytes contain 255indicators. The indicators are numbered sequentially from zero. The fi rst 100indicators are user indicators, and the remaining indicators are used by the system.The indicators are iocated in the bytes that aiso can be used for the first 16 binaryregisters or the first two decimal registers.10