Introduction: Depending on the addressing mode used, an instruction of 8086 microprocessor can be one to seven byte long. These are: One Byte Instruction Two Byte Instruction Three Byte Instruction Four Byte Instruction Five Byte Instruction Six Byte Instruction Seven Byte Instruction The table shows the general format of 8086 instructions. The following paragraph gives the different instruction format with examples 1. One Byte Instruction: These instructions in the category uses the implied addressing mode and register mode instruction. The implied mode instruction does not use the operands, and the register mode uses the operand as one register. a. Format-1: implied Type Byte Addressing Mode Format/ Examples 1 Byte Format Implied Addressing Mode Examples OP CODE CLC, CLD, STC, CMC, CBW, DAA, DAS, AAA, AAS, RET, CLI, HLT etc..   Examples REP, REPZ / REPE,  REPNE / REPNZ, LOCK, LODS /

Instruction Format of 8086 The instructions in 8086 are 1 to 7 byte long depending on the addressing mode. The immediate byte may be 8 or 16 bit, and the displacement in an instruction can be 0 bits or 8 bits or 16 bits. The OP CODE and addressing mode designation may be 1 to 2 byte. Where the OPCODE use 2 byte, the first byte is OPCODE and the REG field of 2nd byte indicate the rest 3 bits of the OPCODE. The different bytes of the instruction are designated in the table below. Byte OPCODE Here W=0/1 for 1 byte/2 byte operand; d = 0/1to show that designated register is src/dst. S bit used sign extended 2's complement in which all bits

Introduction: 8080 and 8085 were used for single processor applications. In this sense 8086 is backward compatible with 8080 and 8085. that means when used in minimum mode, its function is similar to 8085, all control signals are generated on chip. But 8086 is an advanced processor and is built for complex applications involving multiprocessor  which generates all the control signals. In maximum mode the control signals are generated by use of 8288 bus controller and 8289 bus arbiter IC. Differences between the Minimum and Maximum mode of operation: Maximum mode Minimum Mode When pin 33 MN / Mx' is connected to GND. When pin 33  MN/Mx' is connected to high. In maximum mode 8086 generates QS1,QS0,S0' ,S1',S2', LOCK(bar),RQ(bar)/GT1,RQ(bar)/GT0 control signals. and other signals are generated with

Bus Cycle A bus cycle or machine cycle defines the sequence of events when the MPU communicates with an external device such as memory or I/O, which starts with an address being output on the system bus followed by a read or write data transfer. An instruction cycle consists of : A program consists of number of instructions which are stored in memory. These instructions are to be fetched from the memory and decoded to generate the necessary timing and control signals, an instruction may also contain data or a reference to a data that are also required to be read and then the CPU carries out the execution on these data items. Accordingly an instruction cycle consists of following operations: Instruction

L-1 Introduction to microrocessor                                                                                  L-2 PIN Diagram of 8085   L-3 internal architecture 8085                                                                                        L-4 Demultiplexing   L-5-8085Timing Diagram                                                                                               L-6 Memory Organization 8085   L-7B Interrupts Structure of 8085