SHR is a logical shift right instruction used for unsigned operands. There are two shift right instructions namely logical shift right (SHR) and Arithmetic shift right (SAR). The AND operation between these two numbers give: Format : AND Destination, Source AND Logic Example If both input bits are 1, only then AND operation will generate 1 as an output bit. However, the content of the source operand remains unchanged. It ANDs each bit of source operand with the destination operand and stores the result back into the destination operand. Both source and destination operands cannot be a memory location. The source can be an immediate, register, or a memory location and the destination can be either a register or a memory location. The AND instruction perform logical AND operation between two operands. 8086 Arithemtic Right Shift Instruction.Right Shift Instruction Assembly Example 1.Generally you cannot access these registers directly, the way you can access AX and other general registers, but it is possible to change values of system registers using some tricks that you will learn a little bit later. To transfer control to other parts of the program. This allows to determine the type of the result, and to determine conditions IP register always works together with CS segment register and it pointsįlags register is modified automatically by CPU after mathematical operations, flags register - determines the current state of the microprocessor.Other general purpose registers cannot form an effective address!Īlso, although BX can form an effective address, BH and BL cannot. The address formed with 2 registers is called an effective address.īy default BX, SI and DI registers work with DS segment register This is good, since this way we canĪccess much more memory than with a single register that is limited to 16 bit values.ĬPU makes a calculation of physical address by multiplying the segment register by 10hĪnd adding general purpose register to it (1230h * 10h + 45h = 12345h): For example if we would like to access memory at the physicalĪddress 12345h (hexadecimal), we should set the DS = 1230h and Segment registers work together with general purpose register to accessĪny memory value. pointing at accessible blocks of memory. The segment registers have a very special purpose Segment registers, this is never a good idea. SS - points at the segment containing the stack.Īlthough it is possible to store any data in the.ES - extra segment register, it's up to a coder to define its usage.DS - generally points at segment where variables are defined.CS - points at the segment containing the current program.Purposes which limit their use as variables, but theyĪre still an excellent place to store temporary data of Register sets are very small and most registers have special Therefore, you should try to keep variables in the registers.
Requires the use of a system bus, so it takes much longer.Īccessing data in a register usually takes no time. the same is for other 3 registers,īecause registers are located inside the cpu,
Registers 16 bit register is also updated, and vice-versa. therefore, when you modify any of the 8 bit Like: 0011000000111001b (in binary form), or 12345 in decimal (human) form.Ĥ general purpose registers (AX, BX, CX, DX) are made of two separate 8 bitĪnd AL= 00111001b. the size of the above registers is 16 bit, it's something The usage for each general purpose register.
It is assumed that you have some knowledge about number representation (hex/bin),Īssembly language is a low level programming language. Through this document in order to study emu8086 syntax. Programming language (java, basic, c/c++, pascal.) that may help you a lot.īut even if you are familiar with assembler, it is still a good idea to look of course if you have knowledge of some high level This tutorial is intended for those who are not familiar with assembler at all, 8086 assembler tutorial for beginners (part 1) 8086 assembler tutorial for beginners (part 1)
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