Unit 1: Microprocessor and Applications

Intel released the 8085, its follow-up to the 8080, in March 1976.  It was popular as an embedded controller, finding use in scales and other computerized equipment. The 8085 ran at 5MHz and contained 6,500 transistors. It was built on a 3-micron process and incorporated an 8-bit data bus. The microprocessor is the engine of the pc; without them, pcs would not exist. From a technology point of view, a microprocessor is a cpu on a chip. The first one was introduced in 1971, which makes them about 20 years old.

Microprocessor:

Microprocessors are simply a computer processor that has been configured into the design and function of a microchip. Sometimes referred to as a logic chip, this small component functions as the means of executing the command to start booting up a computer. As part of the process, a microprocessor initiates the activation of all the components necessary to allow the computer to be used, such as waking the operating system.

The basic functionality of a microprocessor is all based on the inherent ability to respond to and generate mathematical and logical operations. This function of small computer processors is made possible with the use of registers. Within the registers resides all the data required by the microprocessor to execute such basic functions as addition and subtraction. The configuration of the registers also allow the microprocessor to handle tasks such as comparing two different numbers, and retrieving numbers from various areas and redistributing them.

At the core of the design for the microprocessor is a series of logical instructions that regulate the order that tasks are received and executed. The presence of the instructions assure that tasks are carried out in a sequence that will flow from the completion of one task and into the logical initiation of the next task in the sequence. For example, when an end user boots up a computer, the first instruction that the microprocessor will execute is the activation of the BIOS, or basic input/output system. From that point, the BIOS will load the operating system into the active memory and move on to the next task in the starting process. Each successive task will be achieved once the previous task is complete.

 This is about as simple as a microprocessor gets. This microprocessor has:

• an address bus (that may be 8, 16 or 32 bits wide) that sends an address to memory
• a data bus (that may be 8, 16 or 32 bits wide) that can send data to memory or receive data from memory
• a RD (Read) and WR (Write) line to tell the memory whether it wants to set or get the addressed location
• a clock line that lets a clock pulse sequence the processor
• A reset line that resets the program counter to zero (or whatever) and restarts execution.

Understanding Microprocessors - Video:

Evolution Of Microprocessors:-

A microprocessor is the heart, the soul as well as the brain of a computer. In fact, it is a computer in itself. The evolution of the microprocessor has been one of the greatest achievements of our civilization.

The History Of Microprocessors - Video:

8085 CPU:-

Intel 8085 microprocessor is the next generation of Intel 8080 CPU family. In addition to being faster than the 8080, the 8085 had the following enhancements:

• Intel 8085 had single 5 Volt power supply.
• Clock oscillator and system controller were integrated on the chip.
• The CPU included serial I/O port.
• Two new instructions were added to 8085 instruction set.

       The CPU also included a few undocumented instructions. These instructions were supposed to be a part of the CPU instruction set, but at the last moment they were left undocumented because they were not compatible with forthcoming Intel 8086.

8085  - Video:

Diagram of 8085 Architecture:

It consists of various functional blocks:

Control Unit:

Generates signals within uP to carry out the instruction, which has been decoded. In reality causes certain connections between blocks of the uP to be opened or closed, so that data goes where it is required, and so that ALU operations occur.

Arithmetic Logic Unit:

The ALU performs the actual numerical and logic operation such as ‘add’, ‘subtract’, ‘AND’, ‘OR’, etc. Uses data from memory and from Accumulator to perform arithmetic. Always stores result of operation in Accumulator.

Registers:

The 8085/8080A-programming model includes six registers, one accumulator, and one flag register, as shown in Figure. In addition, it has two 16-bit registers: the stack pointer and the program counter. They are described briefly as follows.

The 8085/8080A has six general-purpose registers to store 8-bit data; these are identified as B,C,D,E,H, and L as shown in the figure. They can be combined as register pairs - BC, DE, and HL - to perform some 16-bit operations. The programmer can use these registers to store or copy data into the registers by using data copy instructions.

Accumalator:

The accumulator is an 8-bit register that is a part of arithmetic/logic unit (ALU). This register is used to store 8-bit data and to perform arithmetic and logical operations. The result of an operation is stored in the accumulator. The accumulator is also identified as register A.

Flags:

The ALU includes five flip-flops, which are set or reset after an operation according to data conditions of the result in the accumulator and other registers. They are called Zero(Z), Carry (CY), Sign (S), Parity (P), and Auxiliary Carry (AC) flags; they are listed in the Table and their bit positions in the flag register are shown in the Figure below. The most commonly used flags are Zero, Carry, and Sign. The microprocessor uses these flags to test data conditions.

For example, after an addition of two numbers, if the sum in the accumulator id larger than eight bits, the flip-flop uses to indicate a carry -- called the Carry flag (CY) -- is set to one. When an arithmetic operation results in zero, the flip-flop called the Zero(Z) flag is set to one. The first Figure shows an 8-bit register, called the flag register, adjacent to the accumulator. However, it is not used as a register; five bit positions out of eight are used to store the outputs of the five flip-flops. The flags are stored in the 8-bit register so that the programmer can examine these flags (data conditions) by accessing the register through an instruction.

These flags have critical importance in the decision-making process of the microprocessor.

The conditions (set or reset) of the flags are tested through the software instructions.

For example, the instruction JC (Jump on Carry) is implemented to change the sequence of a program when CY flag is set. The thorough understanding of flag is essential in writing assembly language programs.

Program Counter(PC):

This 16-bit register deals with sequencing the execution of instructions. This register is a memory pointer. Memory locations have 16-bit addresses, and that is why this is a 16-bit register.

The microprocessor uses this register to sequence the execution of the instructions. The function of the program counter is to point to the memory address from which the next byte is to be fetched. When a byte (machine code) is being fetched, the program counter is incremented by one to point to the next memory location

Stack pointer(SP):

The stack pointer is also a 16-bit register used as a memory pointer. It points to a memory location in R/W memory, called the stack. The beginning of the stack is defined by loading 16-bit address in the stack pointer. The stack concept is explained in the chapter "Stack and Subroutines."

Instruction Register/Decoder:

Temporary store for the current instruction of a program. Latest instruction sent here from memory prior to execution. Decoder then takes instruction and ‘decodes’ or interprets the instruction. Decoded instruction then passed to next stage.

Memory address register:

Holds address, received from PC, of next program instruction. Feeds the address bus with addresses of location of the program under execution.

Control Generator:

Generates signals within uP to carry out the instruction which has been decoded. In reality causes certain connections between blocks of the uP to be opened or closed, so that data goes where it is required, and so that ALU operations occur.

Register Selector:

This block controls the use of the register stack in the example. Just a logic circuit which switches between different registers in the set will receive instructions from Control Unit.

General Purpose Register:

uP requires extra registers for versatility. Can be used to store additional data during a program. More complex processors may have a variety of differently named registers.

Block Diagram of 8085 - Video: