Select Listing of IBM Mainframe Instructions Useful to Know
Flow of control instructions - provide tests and branches to alter which instruction is fetched and executed next often based on an operation instruction; note that all of the instructions below are extended mnemonics of BC - Branch of Condition.
| Instruction | Description |
|---|---|
| B addr | Branch - unconditional branch to addr Used in examples in Modules 3, 5. |
| BH addr | Branch High - conditional branch to addr if greater than |
| BL addr | Branch Low - conditional branch to addr if less than |
| BE addr | Branch Equal - conditional branch to addr if equal to |
| BNH addr | Branch Not High - conditional branch to addr if less than or equal to |
| BNL addr | Branch Not Low - conditional branch to addr if greater than or equal to |
| BNE addr | Branch Not Equal - conditional branch to addr if not equal to |
| BP addr | Branch Positive - conditional branch to addr if result > 0 |
| BM addr | Branch Minus - conditional branch to addr if result < 0 |
| BZ addr | Branch Zero - conditional branch to addr if result = 0 |
| BO addr | Branch Overflow - conditional branch to addr if overflow |
| BNP addr | Branch Not Positive - conditional branch to addr if result <= 0 |
| BNM addr | Branch Not Minus - conditional branch to addr if result >= 0 |
| BNZ addr | Branch Not Zero - conditional branch to addr if result != 0 |
| BNO addr | Branch No Overflow - conditional branch to addr if no overflow |
Data movement instructions - moves data in registers and/or memory.
| Instruction | Description |
|---|---|
| ICM | Insert characters under mask |
| L | Load |
| LA | Load address |
| LH | Load half-word |
| LHI | Load half-word immediate |
| LTR | Load and test register (set condition code) |
| LR | Load register (no change to condition code) |
| MVC | Move characters |
| MVCL | Copy or fill consecutive bytes of memory |
| MVI | Move immediate |
| ST | Store data from register to memory |
| STCM | Store character data from register to memory, using a mask |
Operation instructions - performs arithmetic and logic operations on data and sets condition codes used in conditional branches.
| Instruction | Description |
|---|---|
| A | Add |
| AH | Add signed half-word |
| AP | Add packed decimal number to a packed decimal number |
| AR | Add registers |
| CH | Compare signed half-word |
| CLC | Compare logical characters |
| CLI | Compare Logical Immediate |
| CLCL | Compare character long |
| CP | Compare packed decimal number to packed decimal number |
| CR | Compare signed value in Registers |
| D | Divide |
| DP | Decimal integer division (in packed decimal) |
| MP | Multiply packed decimal number to a packed decimal number |
| OI | Logical OR of a byte |
| S | Subtract |
| SH | Subtract signed half-word |
| SP | Subtract packed decimal number from a packed decimal number |
| SR | Subtract registers |
| SRP | Shifts digits of packed decimal number |
| XR | Exclusive or |
| ZAP | Set packed decimal number to 0 and then add another packed decimal number (so basically a move) |
Data type conversion instructions - converts data from one format to another.
| Instruction | Description |
|---|---|
| CVB | Convert packed decimal number to signed binary integer |
| CVD | Convert signed binary integer to packed decimal number |
| PACK | Convert zoned decimal number to packed decimal number |
| UNPK | Convert packed decimal number to zoned decimal number |
Assembler instructions - instructions to the assembler that are not converted to machine instructions but used during the process of assembling.
| Instruction | Description |
|---|---|
| USING | Specifies which register to use as the base register in a program |
| DROP | Assembler instruction to undefine previous USING instruction |