two operands, requires first negating the subtrahend. A Group 1 OPR instruction that has none of the microprogrammed bits set performs no action. The programmer can write NOP (No Operation) to assemble such an instruction. Group 2, Or Group 00 01 02 03 04 05 06 07 08 09 10 11 ___ | 1| 1| 1| 1| | | | | 0| | | 0| |__|__|__|__|__|__|__|__|__|__|__|__| |CLA SZA OSR SMA SNL HLT 2 1 1 1 3 3 7600 – CLA – Clear AC 7500 – SMA – Skip on AC < 0 (or group) 7440 – SZA – Skip on AC = 0 (or group) 7420 – SNL – Skip on L ≠ 0 (or group) 7404 – OSR – logically 'or' front-panel switches with AC 7402 – HLT – Halt When bit 8 is clear, a skip is performed if any of the specified conditions are true. For example, "SMA SZA", opcode 7540, skips if AC ≤ 0. A Group 2 OPR instruction that has none of the microprogrammed bits set is another No-Op instruction. Group 2, And Group 00 01 02 03 04 05 06 07 08 09 10 11 ___ | 1| 1| 1| 1| | | | | 1| | | 0| |__|__|__|__|__|__|__|__|__|__|__|__| |CLA SNA OSR SPA SZL HLT 2 1 1 1 3 2 7410 – SKP – Skip Unconditionally 7610 – CLA – Clear AC 7510 – SPA – Skip on AC ≥ 0 (and group) 7450 – SNA – Skip on AC ≠ 0 (and group) 7430 – SZL – Skip on L = 0 (and group) When bit 8 is set, the Group 2, Or skip condition is inverted, via De Morgan's laws: the skip is not performed if any of the group 2, Or conditions are true, meaning that all of the specified skip conditions must be true. For example, "SPA SNA", opcode 7550, skips if AC > 0. If none of bits 5–7 are set, then the skip is unconditional. Group 3 Unused bit combinations of OPR are defined as a third Group of microprogrammed actions mostly affecting the MQ (Multiplier/Quotient) register. The MQ register and the extended arithmetic element (EAE) instructions are optional and only exist when EAE option was purchased. 00 01 02 03 04 05 06 07 08 09 10 11 ___ | 1| 1| 1| 1| | | | | | | | 1| |__|__|__|__|__|__|__|__|__|__|__|__|