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

Skip Conditional (PSKC)0 5 8 9 15Op code R F Conditions01 0 0 11 1 1 1 1 1 1 14 8 X XThe skip conditional instruction (PSKC) skips the one-word instruction that immediatelyfollows the PSKC instruction only if certain conditions are present. These conditions arespecified within the PSKC instruction. Since only one word is skipped, the PSKC instrutionshould never be followed by a long-format instruction. Any combination of testingcan be requested.The programmer determines what tests are conducted to decide whether a skip will betaken. This is accomplished by setting bits on or off in the condition field (bits 8 to 15)of the instruction.The bits and their meanings are shown below:Bit Set On Condition Tested9 Carry and overflow indicators both off10 Zero-result indicator on11 Negative-result indicator on12 Positive-result indicator on13 Even-result indicator on14 Carry indicator off15 Overflow indicator offIf any one of the specified test conditions is present, the skip takes place by incrementingthe IAR by 1 before the next instruction is fetched from storage. If none of thespecified test conditions are present, or no conditions are tested (all condition field bitsare set to 0's), the instruction sequence does not skip the next word, but rather executesthe instruction contained in the next word.The R field is ignored in this instruction.The PSKC instruction does not change the carry and result indicators. Testing theoverflow indicator with bit 15 always set the overflow indicator off unless condition fieldbit 8 (overflow-save flag) of the instruction is set on. Testing the overflow indicator withbit 9 does not change the overflow indicator; the overflow-save flag has no effect.Example 1:0 5 8 9 15PSKC instruction0iOp code1 0 0 1i 11R'IIF0Conditions0 0 0 1 0 0 0 0!I'M4 8 0 0No testing is requested since all condition field bits are O's. No skip occurs.