16 bit Assembly
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J... - Jump (conditional) Instruction
The J... instruction actions a conditional jump which generally follows a CMP instruction or an action that sets the flags (like DIV, MUL etc..).
This command has 2 parts, Instruction, then either a Register, Immediate value or a memory address.
These 8 bit near jumps can jump up to 127 bytes forward or backward. Forward start at 0 to 79h, backward start from FF to 80h.
There are 32 J instructions, there can more than one letter following the J which denote the use.
Many of these have the same or similar effects and therefore share the same Op Code.
- O = Overflow Flag
- C = Carry Flag
- S = Sign Flag
- P = Parity Flag
- N = Not that action
- E = Equals
- L = Lower than
- G = Greater than
- Z = Zero value
- A = Above
- B = Below
Syntax: JE 0x03 ; Jump if Equal 3 bytes forward.
Instructions in Op Code sequence
| Operates On | Instruction |
|---|---|
| 70 | JO |
| 71 | JNO |
| 72 | JB, JC, JNAE |
| 73 | JNB, JNC, JAE |
| 74 | JZ, JE |
| 75 | JNZ, JNE |
| 76 | JBE, JNA |
| 77 | JA, JNBE |
| 78 | JS |
| 79 | JNS |
| 7A | JP, JPE |
| 7B | JNP, JPO |
| 7C | JL, JNGE |
| 7D | JNL, JGE |
| 7E | JLE, JNG |
| 7F | JG, JNLE |
| E3 | JCXZ, JECXZ |
Instructions according to use
| Op Code | Instruction |
|---|---|
| Carry | JC, JNC |
| Overflow | JO, JNO |
| Parity | JP, JNP, JPE, JPO |
| Sign | JS, JNS |
| Lower | JL, JB, JLE, JNA, JNG, JNGE, JNAE, JBE |
| Greater | JG, JA, JGE, JNB, JNL, JNLE, JNBE, JAE |
| Equal | JE, JNE |
| Zero | JZ, JNZ, JCXZ, JECXZ |
Last Update 06/02/2023