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

STATE CONTROL INSTRUCTIONSLevel Exit (PLEX)0 5 8 15Op code R Zeros0 0 1 1 0 * * 0 0 0 010 0 0 0III! 1 13 0 0 0The processor exits the current priority interruption level. If lower-level interruptionsare pending, the system remains active and services the request on the highest pendingpriority level. If no other interruptions are pending, the processor enters the wait state.The PLEX instruction does not change the carry, overflow, and result indicators.Stop (PSTP)0 5 8 15Op code R Zeros0 0 1 0 0 • 0 0 0 010 0 0 0!III I I 1 1 1 1 12 0 0 0The processor enters the stop state, provided the System/7 console controls switch is in theenable position. If this switch is not in the enable position, the PSTP instruction performsas a no-operation instruction.The PSTP instruction does not change the carry, overflow, and result indicators.Supervisor Call (SVC)0 5 8 151 0 0 1 11 11I I I I9 8 ReservedThe summary mask is turned on and a branch is taken via the contents of main storagelocation hex 0009. The sequence indicator in the processor status word is turned on.No other indicators are changed. Power/thermal warning interruptions are inhibitedduring this instruction. The contents of the instruction address register (IAR) are storedIn the address specified by the interruption level transfer vector (ILTV) for the levelthat is executing. For example, if the SVC is issued on level 3, the contents of the IAR(the IAR points to the location of the SVC) are stored in the address specified by thecontents of main storage location hex 0013.To allow the system to respond to as many error conditions as possible, the loadprocessor status (PLPS) instruction must be executed after the SVC instruction. If not,a machine check or program check condition causes a machine check class interruption.For example, assume that an SVC instruction has been issued and a PLPS has not beenexecuted. If a program check condition occurs or another SVC is fetched from mainstorage, the processor status word (PSW) is first cleared, then set with the appropriateprogram check condition along with control check. If a second SVC is being fetched, aprogram check condition is set. The setting of control check causes a machine check classinterruption if the keyswitch is in the disable position or the check control switch is inProcessor Instructions 4-51