| Octal Order Code | Nmenonic | Execution |
|---|---|---|
| 070 | CALL X N | Subroutine Entry The CALL instruction causes control to be transferred to the location specified in the operand field. The address of the location immediately following the CALL statement (the link address), and the state of V and zero suppression mode, are automatically stored in the accumulator X (the link accumulator). The format of the link accumulator depends on the address mode and branch mode in which the program member is operating. The contents of the link accumulator should be preserved while the subroutine called is being performed, in order to provide for re-entry to the main program (see the EXIT instruction). C is not used and will be left clear. V is used and will be left clear. Modification This statement has no M field. |
| 072 | EXIT X N | Leave Subroutine The EXIT instruction causes control to be transferred to the location whose address is formed by adding the value specified by N to the link address contained in X. The link address is determined from X in accordance with the address mode and branch mode in which the program member is currently operating. If the program member is operating in compact mode and direct branch mode (15AM and DBM), bits 9 to 23 of X are taken as the link address. If the program member is operating in extended data mode (22AM), or in compact mode and extended branch mode (15AM and EBM), bits 2 to 23 of X are taken as the link address. The address to which control will be transferred will thus be N words beyond the address held in accumulator X, therefore avoiding parameters (if any) held in locations following the CALL instruction. Zero suppression mode is left set to the value stored in the link accumulator, X. If the program member is operating in compact mode and direct branch mode (15AM and DBM), bit 8 of X is taken to represent the value to which zero suppression mode is to be set. If the program member is operating in extended data mode (22AM), or in compact mode and extended branch mode (15AM and EBM), bit 1 of X is taken as representing the value to which zero supression mode is to be set. C is not used and will be left clear. V is left set by the EXIT instruction if either V was left set by the previous instruction or V was set on entry to the subroutine or if both these conditions apply; otherwise V is left unset. Modification The EXIT statement has no M field. |
| 074 (X=0) |
BRN N | Unconditional Branch The BRN instruction results in an unconditional branch to the location specified by N. C is not used and will be left clear. V is not used and remains unchanged. Modification The BRN statement has no M field. |
| 074 (X=1) |
BVS N | Branch if V Set The BVS instruction tests the state of the Overflow register (V), and if set causes a branch to the location specified by N. If V is not set the program continues to the next instruction. C is not used and will be left clear. V is used and remains unchanged. Modification The BVS statement has no M field. |
| 074 (X=2) |
BVSR N | Branch if V Set; Leave V Clear The BVS instruction tests the state of the Overflow register (V), and if set causes a branch to the location specified by N. If V is not set the program continues to the next instruction. C is not used and will be left clear. V is used and is left clear. Modification The BVSR statement has no M field. |
| 074 (X=3) |
BVC N | Branch if V Clear The BVC instruction tests the state of the Overflow register (V), and if clear causes a branch to the location specified by N. If V is not clear the program continues to the next instruction. C is not used and will be left clear. V is used and remains unchanged. Modification The BVC statement has no M field. |
| 074 (X=4) |
BVCR N | Branch if V Clear and Clear V The BVCR instruction tests the state of the Overflow register (V), and if clear causes a branch to the location specified by N. If V is not clear the program continues to the next instruction. C is not used and will be left clear. V is used and will be left clear. Modification The BVCR statement has no M field. |
| 074 (X=5) |
BCS N | Branch if C is Set The BCS instruction tests the state of the Carry register (C), and if set causes a branch to the location specified by N. If C is not set the program continues to the next instruction. C is used and will be left clear. V is not used and remains unchanged. Modification The BCS statement has no M field. |
| 074 (X=6) |
BCC N | Branch if C is Clear The BCC instruction tests the state of the Carry register (C), and if clear causes a branch to the location specified by N. If C is not clear the program continues to the next instruction. C is used and will be left clear. V is not used and remains unchanged. Modification The BCC statement has no M field. |
| 074 (X=7) |
BVCI N | Branch if V Clear; Invert V The BVCI instruction tests the state of the Overflow register (V), and if clear causes a branch to the location specified by N. If V is not clear the program continues to the next instruction. C is not used and will be left clear. V is used and will be inverted (i.e. if it is found clear it will be left set, and if it it is found set it will be left clear). Modification The BRN statement has no M field. |
| 076 | BFP N | Branch State of Floating-Point Accumulator or
Floating-Point Overflow The BFP instruction tests the state of the contents of floating-point accumulator (A) or floating-point overflow (FOVR) and branches on the condition specified by the X address of the operation. The value in the accumulator (X) field determines the condition: X = 0 Branch to N if the content of A equals zero. X = 1 Branch to N if the content of A not equal to zero. X = 2 Branch to N if the content of A is positive or zero (i.e. sign bit of argument = 0). X = 3 Branch to N if the content of A is negative (i.e. sign bit of argument = 1). X = 4 Branch to N if FOVR is clear. X = 5 Branch to N if FOVR is set. FOVR is used (see above) but remains unaltered. C is not used and will be left clear. V is not used and remains unchanged if X = 4 or 5. If X = 0, 1, 2 or 3 V will be set of FOVR is set. Modification The BFP statement has no M field. |