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

Machine CheckMachine check interruptions occur when processor error checking circuits detect a machinemalfunction. Malfunctions can be caused by:1. A parity error in an index register.2. A parity error encountered by the processor attempting to access main storage_3. More than one type of machine cycle requested or taken simultaneously.4. More than one interruption level being executed simultaneously, or no level isactive and the processor is taking machine cycles.5. An I/O hardware error occurring on the internal interface.Note: A machine check error can result from programming if a storage location or anindex register is used by the program and the location or register was not loadedwith an initial value after the system was powered on. A machine check can also resultfrom a software error when a program check is encountered between the execution ofa supervisor call instruction and a load processor status instruction, or when anothersupervisor call instruction is issued.Operator console lights indicate the cause of a machine check when the processor isin the stop state. Only one machine check can occur at any one time in the system.When a machine check interruption occurs, all I/O devices and pending interruptionrequests are reset. The address of the instruction being executed when the error occurredis saved automatically in storage location hex D. The contents of storage location hex B,which contains the starting address of the machine check servicing routine, are then automaticallyloaded into the IAR and the servicing routine is given control. (Refer to"Reserved Storage Locations" in this chapter.)Program CheckProgram check interruptions occur when the processor detects a machine instruction thatis invalid for one of the following reasons:1. Invalid operation code (an invalid instruction for the System/7 processor).2. Invalid modifier field contents in instructions with operation code of 11111. (Onprocessor module model E, this condition causes a no-operation and does not resultin a program check.)3. Invalid address (a main-storage address that exceeds the limits of the storageinstalled in the system).4. Invalid function field (000) in an execute I/O instruction (processor module modelsA and B only).5. Invalid shift count value in shift instructions.6. A cycle steal I/O instruction has been issued and there is no cycle steal featureinstalled in the processor.7. The processor has attempted to alter a storage protected area without the properkey (processor module model E only).When the machine is in the stop state, operator console lights indicate the causeof a program check.