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

Accumulators (ACC 0 to ACC 3)Page of GA34-0003-6, -7As Updated August 20,1976By TNL GN34-0340The System/7 processor has four accumulators (ACC 0 to ACC 3), one for each priorityinterruption level (see Figure 2-2). These 16-bit registers are used in most arithmetic andlogical operations. Such operations are performed using one specified operand (fromstorage or from an index register) and one implied operand (the value previously loadedinto the accumulator). The result is in the accumulator at the end of the operation. Thisresult is obtained by a machine function that depends upon the instruction being executed.The following example illustrates the use of the accumulator:IIII Load one operand into accumulatorStorageOperand AOperand B IAccumulatorOperand A1111 Perform arithmetic operation (such as operand A plus operand B)StorageOperand AAccumulatorOperand A1111 Result of arithmetic operation appears in accumulatorStorageAccumulatorResultNotice that operand A andoperand B are still in theiroriginal storage locationsThe contents of any selected accumulator can be displayed on the operator console ormodified via the console switches.IInterruption Mask Register and Summary MaskThe interruption mask register is a 4-bit register shown in Figure 2-2. The bits arenumbered 0 to 3, each bit corresponding to priority interruption levels 0 to 3, respectively.The appropriate bit in the mask register is set on (given a 1 value), to enable the correspondingpriority interruption level. That is, interrupting sources assigned to that prioritylevel can present interruptions to the system if their priority is higher than that of thecurrent operating program. In addition, there is a summary mask bit which, when on,prevents acceptance of priority interruptions without changing the contents of theinterruption mask register. Power/thermal warning interruptions are also disabled whenthe summary mask is on.IBM 5010 Processor Module 2-11