Systems Reference Library - All about the IBM 1130 Computing ...

Page of GA26-5918-8Revised July 14, 1971By TNL: GN26-0269Arithmetic SignThis light (ARITH SIGN) is on when bit position 0of the accumulator does not initially equal bit position0 of the B-register.Zero RemainderThis light (ZERO REM) is on when the accumulatorcontains a zero balance during a divide instruction.BranchThis light is on during branch instructions.Storage Protect BitThis light (STOR PROT BIT) is on when the storageprotect bit is on in a word transferred between theB-register and core storage.Parity BitThis light (PTY BIT) is on when the parity bit is onin a word transferred between the B-register andcore storage.Interrupt ServiceThis light (INTR SERV) is turned on when an interrupt-forcedBSI instruction is being executed for thehighest priority interrupt level that is on and notmasked.Cycle Steal ServiceThis light (SC SERV) is on during cycle steal operationsfor the highest priority data channel requiringservice.mode, the light will be on at the end of 12, or at theend of IA with indirect addressing, thus indicatingthat the next cycle will access CE storage. At theend of E-cycle, the light will be off, but the M-registerwill display the CE storage address.Operation Code CheckThis light is on when an invalid operation Op codeis placed in the Op register. The Op code check lightis turned off and the check light is turned on (internalinterrupt) at the end of the cycle in which theerror is detected. This allows the Op code checklight to indicate any subsequent error.Note that an Op code check causes an internalinterrupt if the disable interrupt and check stopswitches are off, or a check stop if the check stopswitch is on.Storage Protect CheckThis light (STOR PROT CHECK) is turned on whenan attempt is made to write in a read-only corestorage location. The storage protect check light isturned off and the check light is turned on (internalinterrupt) at the end of the cycle in which the erroris detected. This allows the storage protect checklight to indicate any subsequent error.Note that a storage protect check causes aninternal interrupt if the disable interrupt and checkstop switches are off, or a check stop if the checkstop switch is on.Parity CheckThis light (PTY CHECK) is turned on when a parityerror (even number of bits on) is detected in the18-bit word transfer between the B-register andcore storage. The parity check light is turned offand the check light turned on (internal interrupt) atthe end of the cycle in which the error is detected.This allows the parity check light to indicate anysubsequent error.Auxiliary StorageThis light (AUX STOR) is on when CE storage (usedfor customer engineer programs and error logs) isbeing accessed.When the system is executing instructions thataccess CE storage from main storage, the AUX STORlight turns on at T7 of the cycle preceding the executecycle and turns off at the last T7 of the operation.When the system is running in a single storage cycleClockThese eight lights (0 through 7) show the advanceof the basic P-C clock each time START ispressed and the mode switch is on SS (singlestop). Normally, pressing START eight timeswith the mode switch on SS is equivalent topressing START once with the mode switch onSSC (single storage cycle).86