Digital Electronics: Principles, Devices and Applications

Microprocessors 54713.10 16-Bit MicroprocessorsEight-bit microprocessors are limited in their speed (the number of instructions that can be executed in1 s), directly addressable memory, data handling capability, etc. Advances in semiconductor technologyhave made it possible for the manufacturers to develop 16-bit, 32-bit, 64-bit and even-larger-bitmicroprocessors. This section describes the block diagram, pin-out configuration and salient featuresof some of the most popular 16-bit microprocessors including 8086 of Intel and Motorola’s MC68000.13.10.1 8086 MicroprocessorThis is a 16-bit microprocessor introduced by Intel. It was designed using HMOS technology andcontains approximately 29 000 transistors. It has a maximum operating frequency of 10 MHz. The 8086,8088, 80186 and 80286 microprocessors have the same basic set of registers and addressing modes.The 8086 microprocessor is available in DIP, CeraDIP and PLCC packages. Figure 13.15 shows ablock diagram of 8086.13.10.1.1 8086 registers8086 has four segment registers and other general-purpose registers. The segment registers includecode segment (CS), stack segment (SS), data segment (DS) and extra segment (ES). The generalpurposeregisters of 8086 include the accumulator register, base register, count register, data register,stack pointer (SP), base pointer (BP), source index (SI) and destination index (DI). The stack pointer,base pointer, source index and destination index registers are both general and index registers. Otherregisters include the instruction pointer (IP) and the flag register containing nine one-bit flags.13.10.1.2 Addressing modesThe addressing modes of 8086 are implied addressing, register addressing, immediate addressing, directaddressing, register indirect addressing, base addressing, indexed addressing, base indexed addressingand base indexed with displacement addressing.13.10.1.3 Internal Architecture and Pin-out ConfigurationThe internal functions of the 8086 processor are portioned logically into two processing units. Thefirst is the bus interface unit (BIU) and the second is the execution unit (EU), as shown in Fig. 13.15.The BIU provides the functions related to instruction fetching and queuing, operand fetch and storeand address relocation. It also provides the basic bus control. The EU receives prefetched instructionsfrom the BIU queue and provides unrelocated operand addresses to the BIU.13.10.1.4 Instruction setThe instruction set includes the following: data transfer operations, arithmetic operations, logicalinstructions, string manipulation instructions, control transfer instructions, processor control instructionsand input/output operations.