1, the instruction is divided into an operation code and address code field , the binary digits
Instruction system different addressing main purpose is to shorten the length of the instruction, to expand the address space, increase programming flexibility.
2, operation type instruction address addressing the transfer type instruction except that the operation of this type means that the operand addressing, and the addressing is metastatic instruction address of the instruction to be executed next.
3, the zero address of the instruction only the opcode, no operands. Such instructions there are two cases: one without operands, the other operand is implicit default operand in the register, the instruction register may be accessed directly .
4, extended operation code is an instruction optimization technique, the number of different addresses may have different operating instruction code length.
5, instruction optimization coding method, coding in terms of efficiency, with a huffman coding enables the average length of the shortest opcode, the highest efficiency.
6, using the increment counter method microinstructions, the address stored in the location of the next microinstruction is a microinstruction address counter in.
7, the machine instruction is the minimum unit of programming available to the user, it is a basic operation of the machine can be completed, a period of machine instructions microprogram microinstruction prepared using FIG . Is a collection of functions specific microinstruction micro-command set, typically expressed in binary coding.
8, microinstruction format , the horizontal microinstruction code usually direct representation, direct field coding method, mixed representation of three ways, each of which represents a direct method that is a microinstruction control signal.
Direct representation: the operating characteristics of the control field of each bit representing a micro-command. The advantage of this method is simple and intuitive, which is directly used to control the output; disadvantage microinstruction word is considerably longer, and thus a large memory capacity of the control.
Coded Representation: i.e. direct encoding method field, the encoded representation is a set of micro-repellency to a command signal to form a group (i.e., a field) and (fields) for each micro decoder command signal is translated by the Panel code, the decode output as an operation control signal.
Mixed notation: is the direct representation of the field coding method in combination in order to consider requirements of the instruction word length, the flexibility, the microprogram execution speed.
9, the I / O command
I / O instructions are part of the CPU instruction system
I / O instruction is a type of machine instructions
I / O instruction reaction characteristics of CPU and I / O devices to exchange information
10, direct branch instruction function is to address code instructions are sent to the PC, the PC will always keep the address of the next instruction to be executed. When the execution order: PC + 1; case when the branch instruction, PC content acquired by the address field of the IR.
11, two address instruction generally includes a type RR, RM type and class 3 MM type address code field of the instruction operand address may be, it may be a register number. Some computers allow one immediate operand is addressed, the address of the instruction code field is stored in the operand.
