8086 register group

There are some working registers in the EU and Biu sections of 8086. These registers are used to store various information in the calculation process, such as the operand address, the operand, and the intermediate result of the calculation. It is much faster for a microprocessor to access data from a register than to access data from a memory. Therefore, in the computing process, it can improve the efficiency of using a register to store the operands, intermediate results, or other information.Program. Based on the functions of these registers, the 8086 register group can be divided into general registers, special registers, and segment registers, as shown in 2.3. These registers are described below.

1. General registers
General registers include eight 16-bit registers: ax, BX, CX, dx, SP, BP, Di, AND Si. Ax, BX, CX, and dx are generally used as common data registers to temporarily store the operations, results, or other information used in the calculation process. They can also be divided into two independent 8-bit registers named Al, ah, BL, BH, Cl, CH, DL, and DH. In addition to common functions, these four general data registers are also used for the following purposes:

Ax is used as the accumulator, so it is the main Register of arithmetic operations. Specify in the multiplication/division command to store the operands. In addition, all I/O commands use ax or Al to transmit information with external devices.

BX can be used as the base address register when calculating the memory address.

CX is often used to store the Count value, such as the shift instruction, loop instruction, and string processing instruction as an implicit counter.
DX and ax can be combined to store a double-character long number during double-character long operation. dx is used to store high 16-bit data. In addition, for some I/O operations, DX can be used to store the I/O port address.

The four 16-bit registers sp, BP, Si, and DI can store the operands in the operation process like the data register, but they can only be used in the unit of words (16 bits. In addition, they are more often used to provide offset addresses when memory addressing. Therefore, they can be called pointers or address change registers.

SP is called the stack pointer register to point out the offset address of the stack top.

BP is called the base address pointer register. It is used as the base address register when addressing, but it must be used with the stack segment register ss to determine the storage unit address in the stack segment.

Si is the source address change register. In the string processing instruction, Si is used together with DS as the hidden source address change register to determine the storage unit address in the data segment, it also has the function of automatic increment and auto increment.

Di is the destination address change register. In the string processing instruction, Di is combined with the additional segment register es to achieve addressing in the additional segment, and then Di is automatically incremental or reduced.