Program Control Instructions. Programme Control Instructions. INTRODUCTIONThe programme control instructions direct the flow of a programme and allow the flow of the. A change in flow often.
CMP or TEST instruction, are followed by a. THE JUMP GROUPThe main type of programme control instruction, the jump.
JMP), allows the programmemer to skip sections of a programme and branch to any. A conditional jump instruction. The results. of these numerical tests are held in the flag bits, which are then tested by. Unconditional. Jump. Three types of unconditional jump instructions are. The short jump is a 2- byte instruction that allows jumps or. The 3- byte near jump allows a branch or jump within ±3.
K. bytes (anywhere) from the instruction in the current code segment. Finally, the. 5- byte far jump allows a jump to any memory location within the entire memory. The short and near jumps are often called intrasegment jumps and the far. Short Jump. Short. This is because a jump address is not stored with.
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Instead of a jump address, a distance, or displacement, follows the. The short jump displacement is a distance represented by a 1- byte signed. When the microprocessor executes a short jump, the. IP) to generate. the jump address within the current code segment. The short jump instruction branches to this new address for the next. Whenever a jump instruction references an address, a label. The JMP NEXT is an example, which jumps to label NEXT.
This is the c programming questions and answers section on 'Control Instructions' with explanation for various interview, competitive examination and entrance test.
We never use an actual hexadecimal address with any. The label NEXT must be followed by a colon (NEXT: ) to allow an. If a colon does not follow a label, you. Note that the only time we ever use a colon after a label is. Near Jump. The. near jump is similar to the short jump except the distance is farther.
A near. jump passes control to an instruction in the current code segment located within. K bytes from the near jump instruction. The near jump is a 3- byte. The signed displacement adds to the instruction pointer (IP) to generate.
Because the signed displacement is in the range of ±3. K, a. near jump can jump to any memory location within the current real mode code. Conditional Jumps.
Conditional jumps are always short jumps in the 8. This limits the range of the jump to within +1. The conditional jump instructions test the following flag. S), zero (Z), carry (C), parity (P), and overflow (0). If the. condition under test is true a branch to the label associated with the jump. If the condition is false, the next sequential step in the programme. The operation of most conditional jump instructions is.
Relative magnitude comparisons require more complicated. Because we use both signed and unsigned numbers, and the. The 1. 6- and 3. 2- bit numbers follow the same order as the. Notice that an FFH is above the 0. H in the. set of unsigned numbers, but an FFH (- 1) is less than 0. H for signed numbers. Therefore, an unsigned FFH is above 0.
H, but a signed FFH is less than 0. H. When we compare signed numbers, we use JG, JE, JGE, JLE. JE, and JNE. The terms greater than and less than refer to signed numbers. When. we compare unsigned numbers, we use JA, JB, JAE, JBE, JE, and JNE.
The terms. above and below refer to unsigned numbers. The remaining conditional jumps test individual flag bits. Notice that JE has an alternative opcode JZ. All. instructions have alternate opcodes. LOOPThe LOOP instruction is a combination of a decrement of CX and a conditional. In the 8. 08. 6, LOOP decrements CX and if CX is not equal to zero, it jumps.
If CX becomes a 0, the next sequential. Conditional. LOOPS. The. LOOP instruction also has conditional LOOPE and LOOPNE. The LOOPE (loop while. CX is not equal to zero, while an equal condition. It will exit the loop if the condition is not equal or if the CX.
The LOOPNE (loop while not equal) instruction jumps if. CX is not equal to zero, while a not equal condition exists. It will exit. the loop if the condition is equal or if the CX register decrements to 0. As. with the conditional repeat instructions, alternates exist for LOOPE and LOOPNE.