The syntax for storage allocation statement for initialized data is − Allocating Storage Space for Initialized Data It can be used to reserve as well as initialize one or more bytes. The define assembler directive is used for allocation of storage space. If AH is greater or equal to CH data, then the program counter will jump to the L1 label.NASM provides various define directives for reserving storage space for variables. Now replace ADD instruction with CMP instruction. Now after the execution of JAE instruction, the program counter will not jump to L1 instead it would execute the next instruction after JAE instruction. As it generates carry, therefore, CF becomes equal to 1. The first instruction adds C9 and 7AH and gives 143. The JAE/JNB/JNC instructions check Carry flag (CF). If CF is 1, then the instructions after label address L2 will undergo execution. If AH is less than the CH, then it will borrow carry thus setting CF to 1. The Compare instruction subtracts the content of CH from AH. If it is 1, the control is transferred to label address. The JB or JBNE instructions check whether CF flag is 1 or not. If the zero flag is 0, then the program counter will jump to the next instruction which is JB L2. If it is 1, the program counter jumps to L1 which will print the message “Equal numbers” on the emulator screen. If the two numbers are equal, zero flag (ZF) will be equal to 1.
PRINT REGISTER VALUE EMU8086 CODE
Even if you don’t use this instruction in the code given below, it will not affect the program execution as if the first two conditions are not satisfied, then it means the number 1 is greater than number 2. The JA instruction will check if CF is 0. MSG2 DB "Number 1 is greater than Number 2$" MSG1 DB "Number 1 is less than Number 2$"
Moreover, if any one of them is 0 and other is 1, then this instruction will have no effect of program execution. Also, if both CF and ZF are equal to 1, then the program will continue to execute sequentially. If both are 0, then the IP will jump to the target address. This code is implemented using three conditional branches which are JE, JB and JA. The code below compares two numbers and print if number 1 is equal, greater or less than number 2. 8086 Microprocessor Assembly Comparison Example Let’s discuss these instructions in detail through examples. These instructions are executed after some other instructions which affects the content of flag registers. Jump if Less than or Equal/Jump if Not Greater Jump if Less Than/Jump if Not Greater Than or Equal Jump if Greater or Equal/Jump if Not Less Than Jump if Greater/Jump if Not Less Than or Equal Jump if Below or Equal/ Jump if Not Above Jump if Below/ Jump if Not Above or Equal Jump if Above or Equal/ Jump if Not Below/Jump if No Carry Table below shows the mnemonics of all the conditional branches instructions. List of 8086 Conditional Branch Instructions If the condition is not satisfied, then the program continues in a sequential manner. The flag conditions are checked depending upon the instruction, if they are true the program control is transferred to the memory address pointed by the IP register.
The target address must be within the -128 to +127 bytes of IP. It is sign-extended to 16-bits and added to the contents of IP register. It is a 2-byte instruction consisting of 1-Byte Opcode and 1-byte Label. The syntax of these instructions is: Opcode LABEL The conditional jumps are also near jumps. In the far jumps, the program counter jumps to the memory location which lies outside the current code segment whereas in near jumps, the IP points to the memory address inside the current code segment and that is why the CS register remains unchanged in near jumps. There are two types of jumps namely Far and Near. It checks one or more flag conditions and transfers the control to a new memory location. On the other hand, the conditional branches are those instructions whose execution is based on some condition. For example JMP NEXT Conditional Branch Instructions
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