Microprocessors: Background

The microprocessor’s role in your computer is pretty clear. It does all your calculations, processes your word documents, and handles your graphics. But how could a contraption so small do so much?

WORKING:

The way a microprocessor works is through Boolean logic. All information is processed in the form of “1″s and “0″s — called the binary system. These are transmitted through electrical signals that are sent through the basis of the chip, the transistors. These transistors are arranged to carry out instructions, and do so by being formed into different “gates” (Boolean Logic, Gates, and Building Computer Circuits).

Microprocessors work by reacting to an input of 0s and 1s (binary signals) in specific ways and then returning the output based on the decision. The decision itself happens in a circuit called logic gate, each of which requires at least one transistor (electronic switches inside the processor), with the inputs and outputs arranged differently by different operations. The fact that today’s microprocessor contain millions of transistors offers a clue as to how complex the logic system is.

The microprocessor’s logic gates work together to make decisions using Boolean logic. The main Boolean logic operators are AND, OR, NOT, and NAND.(we have learned about how to use these logic operators in 311) Logic gates operate via hardware known as a digital switch. The most common type of switch in today’s computer is a transistor known as a MOSFET. The MOSFET performs a simple but crucial function: When voltage is applied to it, it reacts by turning the circuit either on or off. Millions of MOSFET act together, according to the instructions from a program, to control the flow of electricity through the logic gate to produce the required result.

Working of  gates in microprocessor:

There are several types of gates, mainly AND, OR, NOT and XOR (Boolean Logic, Gates, and Building Computer Circuits). The best way to understand these gates is through truth tables. For example, for the AND gate, the output/result (denoted by R) is only “1″, or TRUE if both values plugged in (denoted by P and Q) are “1″. Otherwise the output is “0″, or FALSE

The OR is even simpler. If P OR Q is “1″, then the R is “1″. A truth table would look like this:

The NOT operator just reverses the input. If the input is “1″, then the output is “0″ and vice versa.

The XOR gate is exclusive. That means that if only one of the values is “1″, then the output is “1″. Otherwise, none or both are “1″, then the output is “0″. Notice it’s the same as the OR gate except for when both P and Q are “1″.

So what is the use for all these gates, you may ask. Well, using these gates in combinations, we can process data. Let’s just start out basic and go with a comparison chip. So our target truth table looks like this:

WORKING OF LOGIC GATE THROUGH CIRCIUT DIAGRAM

Simplest of all – the NOT gate, or the logical inverter (see bottom image, lower left corner). The NOT gate has one entrance and one exit and has the role of inverting logic bits. This basically means that when a ‘1′ logic bit is applied on the ‘a’ terminal for example, the ‘c’ terminal must produce a ‘0′ logic bit. The situation is reversed when ‘0′ logic is applied on the ‘a’ terminal by forcing the ‘c’ terminal to output a ‘1′ logic bit. Inversion is one of the basic operations in Boolean logic.

Another logic gate of critical importance is the AND gate (upper left corner), which practically designates an operation similar to multiplying. As you can see, the AND gate has two input terminals (a,b) and an output terminal (c). In fact the number of input terminals is unlimited. Boolean logic puts it very simple. If one of the input values is ‘0′ logic, then the value of the other bits is irrelevant and the output will always produce a ‘0′ logic. A ‘1′ logic bit is present at the output terminal, only when all input bits are equal to ‘1′ logic.

The OR gate, operates according to the logic that if one of the input terminals bears a ‘1′ logic bit, then the ‘c’ terminal will always produce a ‘1′. The situation revers the truth table for a single pair of bits and determine which of the corresponding terms (expressed using the names of the inputs) are needed to write the logical expression used to express equality. [Note the use of the apostrophe (') following the input label to indicate the complement of the input bit]. The equality circuit should output a 1 (or true), only if the

two bits at the inputs of the circuit are identical (both 0 or 1). The truth table looks like this:

        Inputs   Output

        ======   ======

         A  B    Result Term

         0  0      1    A'B'

         0  1      0    A'B

         1  0      0    A B'

         1  1      1    A B

Collect those terms where the result is 1 and OR them together. This is the logic function we seek to create using our logic gates.

Logical function = A’B'+ AB {determines equivalence of a single pair of bits}

A single AND gate with the indicated bits or their complements as inputs. So to implement the function above, you need two AND gates (one for each term), two NOT gates (to get the complement of the input bits), and one OR gate (to combine the outputs of the AND gates. The output of this OR gate is the result we seek.

The circuit above compares only two bits of the two binary representations. To compare all the bits in the two binary items, we would need one copy of circuit above for each bit in the binary value. Each copy of the circuit would get a single pair of corresponding bits, one bit from each of the two binary values being compared. All of the outputs of each of the circuits above would be ANDed together in another circuit to determine if all the bita

This “grand AND” would output a single one if every bit in a byte matches the corresponding bit in the other byte to which it is being compared.

The circuit shown below is the complement of the equivalence circuit. This circuit is also frequently encountered in computer applications, so it is given a special name:

es when all of the input bits are ‘0′ logic. The NAND (NOT AND) and NOR (NOT OR) gates can be imagined as an AND respectively an OR gate to whose output terminals a NOT gate (see image for symbols) is connected. Their logic is basically identical to that of AND and OR gates, but the output value is always reversed.

SCINTIST WORKING ON MICROPROCESSOR

Each of the three researchers — Todd Mowry, Ph.D., David Patterson, Ph.D., and Euisik (”James”) Yoon, Ph.D. — will provide SandCraft with a window into future computer processing technologies and provide guidance on the development of advanced architectures.

Dr. Patterson, a member of University of California at Berkeley faculty since 1977, led the research and design program for RISC 1, which became the foundation for the SPARC architecture. He is currently directing projects in large scale computing using networks of workstations, and the development of novel microprocessors using intelligent DRAM (IRAM). SandCraft has provided Patterson’s student design-team with access to an early version of the design database for its own RISC processor core, the SR1.

“SandCraft’s approach to processor design recognizes that the most exciting opportunities for innovation lie in media-rich consumer appliances and other non-traditional computing systems,” said Dr. Patterson. “The company is pushing the performance of an industry-leading RISC architecture, and it is a real benefit to our students to have the opportunity to see the development work as it occurs.”

Norman Yeung, president and CEO of SandCraft, described the newly formed Technical Advisory Board as a resource that will provide additional insight on developments in processor architecture and requirements for advanced systems. This outside perspective complements the company’s in-house research and development programs and helps to create a balance between the immediate requirements of System-on-Chip (SoC) product development and the longer-term definition of new approaches to technology and processor design.

“SandCraft’s success is based on its ability to focus on implementation of processor designs to power the next generation of consumer electronics and high-performance embedded computing systems, and to deliver these designs to licensees as cores or complete integrated circuit designs,” said Yeung.