IBM System/7 Functional Characteristics - All about the IBM 1130 ...

Read 1SW0 5 8 11 16 20 26 31Op code R Fun Zeros Mod DA MA0 0 0 0 1 X X X 0 1 0 0 0 0 0 0 0 0 1 1 0 0 1 0 0 0 0 0 0 0 0 01111 ii 11 Ilil 111 11111 111110 8-F 4 0 3 2 0 0The read ISW command stores the operator station ISW into the index register specifiedby the R field, or the accumulator if R=000.Interrupt Status Word (ISW): The 16 bits in the interrupt status word are set to indicateoperating status of the operator station and to request service from the processor.Interruptions result from setting any ISW bit except the busy and printer paper low bits. Ifthe ISW is successfully read, the ISW is reset if the interruption request is accepted by thesystem. The ISW is also reset by a system reset, or by the first new selection of the operatorstation by a command (not necessarily read ISW) after the interruption has been acceptedby the system.Significant bits in the ISW and their meanings are:Significant Bits Meaning0 Attention. The operator station request key was pressed. If the operatorstation adapter is not busy and no interruption is pending, the adapterpresents an interruption request. If the adapter is busy or has aninterruption pending, the attention interruption bit will be presentedin the ISW along with the device-end bit when the end interrupt occurs.3 End of message. The EOM (end of message) key on the operatorstation was depressed. This status bit also sets ISW bit 13 and presentsan interruption request to the processor.12 Device busy. The operator station motor is reaching operating speed,or a command has been issued that will result in an interruptionrequest, which has not yet occurred.13 Device end. The operator station has performed the requestedoperation or requires service from the processor.15 Printer paper low. Indicates that the paper supply in the 5028 is low.This bit is reset by adding more paper; it is not reset by a read ISWcommand.