Intel 8255 (Programmable Peripheral Interface)

Intel 8255 is a PPI (Programmable Peripheral Interface) and is used to interface Peripheral devices to microcomputers. It can be programmed in a variety of ways as per Programmer Requirements. It has two versions 8255A and 8255B. Both of them are similar in general description but are different in their electrical characteristics.

Intel 8255 Consists of Three 8 Bit Ports: Port A, Port B and Port C. The Port C is further divided into two 4 Bit Ports: Port C_UPPER and C_LOWER. These three ports are divided into two groups for the purpose of Programming:

Group A: This Includes Port A (PA₀-PA₇) and 4 MSBs of Port C (PC₄-PC₇).

Group B: This Includes Port B (PB₀-PB₇) and 4 LSBs of Port C (PC₀-PC₃).

Features of 8255A (PPI)

It is a 40 pin IC.
It Operates on single +5V_DCsupply.
Power Dissipation=1 watt.
Ambient Temp. =0- 70 °C
Input Low Voltage (V_IL) = Min. 0.5V, Max. 0.8V.
Input High Voltage (V_IH) =Min. 2V, Max. V_CC.
Output Low Voltage (V_OL) = 0.45V
Output High Voltage (V_OH)= 2.4V
Voltage on any pin 0.5V to 7V.
Darlington Drive Current= Min. 1mA, Max. 4mA.

Pin Description of 8255A

Pin	Description
D0-D7	8 Bit Bidirectional Data Bus and goes to tri state condition if CS is high.
	Chip Select Signal. 8255 is Selected if this pin status is low.
A0-A1	Used to select port from which data is to be transmitted or to which data is to be transmitted.
	Port/Control Word Register	Port/Control Word Register Address
	Port A	00
	Port B	01
	Port C	02
	Control Word Register	03
	To indicate read operation
	To indicate write operation.
PA0-PA7	8 Pins of Port A
PB0-PB7	8 Pins of Port B
PC0-PC3	4 Pins of Port C LOWER
PC4-PC7	4 Pins of Port C UPPER
VCC	+5V DC Supply.
GND	Ground Signal

Operating Modes of 8255A

User Defined Data Types in C++

The third type of data type in C++ is user defined. Following are some user defined data types:

Structure:  Collection of data elements grouped under one name is called Structure. Different data elements are called members and can have different data type of different length.

Declaration

Struct Student
{
Int roll_no;
Float marks;
} BA, BSC, BCOM;

In this example Student is declared as Structure with members roll_no and marks. BA, BSC, BCOM are the objects of structure Student. Here roll_no is declared as integer and marks as float, which are fundamental data types.

Class: Extended version of Structure is called Class. Structure holds only data whereas class can hold both data and functions. Another concept of access specifier is also added to it which uses three keywords Public, Private, Protected. Access Specifier modifies access rights as:

Public: Public members can be accessed anywhere where object is visible.
Private:Private members can be accessed only by other members of same class or by their friend functions.
Protected:Protected members can be accessed by other members or same class, their friend functions and by elements of derived classes of same class.

Overclocking

Operating a Chip at higher clock speed than its rated clock speed is called Overclocking. CPU Clock speed is the product of FSB (Front Side Bus) Clock and clock multiplier. Overclocking is achieved by either increasing FSB Clock or Clock multiplier or either by increasing both.

Need of Overclocking

The idea behind the use of Overclocking concept is to increase the system performance at no cost or very little cost. We can Overclock a processor by just changing some settings on motherboard or in CMOS setup. The main considerable point in Overclocking is heat. Processor can only be overclocked if and only if proper cooling is there. E.g. Pentium 4 @2.0 GHz Processor can be overclocked to gain 2.2 GHz Clock speed.

Is it Risky?

Derived Data Type in C++

The Data type that is derived from fundamental data types is called derived data type. Some of them are explained below:

 Array:  An array is a collection of homogeneous type of data. It is a named list of finite numbers of data elements. In array each data element is referenced by a set of consecutive numbers i.e. 1, 2, 3……n. If TECH is an array of five elements than its elements will be referenced as: TECH [1], TECH [2], TECH [3], TECH [4], TECH[5]. An Array can either be one dimensional, two dimensional or multidimensional.

Functions: Self contained block of program that performs a coherent task of some type is called Function. These are used because of following reasons:

Fundamental Data Types in C++

These are those data types that are not composed of any other data types. C++ makes use of following five fundamental data types
1) Char: This data type is used to store basic character sets. It is sometimes referred to as integer type because letters and symbols are represented in memory by the associated number codes. Table given below illustrates various types of character types along with their range.

Character Type	Size in Bytes	Minimal Range
Char	1	-128 to 127
Unsigned Char	1	0 to 255
Signed Char	1	-128 to 127

2) Int:These are whole numbers and do not

Internetwork Packet Exchange (IPX)

Internetwork Packet Exchange (IPX) is a connectionless datagram protocol that is used by the Novell NetWare Operating System.  This protocol is the implementation of Xerox Network Systems’ IDP (Internet Datagram Protocols). It is Layer 3 protocol i.e. Network Layer Protocol.

IPX Protocol is very similar to the IP protocol. Some useful points about this protocol are as follows:

1)Unique 32 bit address is assigned to Logical Networks ranging from 0x1 to 0xFFFFFFFF (Hexadecimal).

2)48 bit node address is used by hosts, which is by default set to network card’s MAC address. Node address and network address are jointly used to identify the host on network.

3)00:00:00:00 means current network.

4)FF: FF: FF: FF is used as broadcast address.

Figure Given below Illustrates the IPX Packet.

Cheksum : Its value is set to FFFFH

Computer Codes

1)   BCD (Binary Coded Decimal) Code:  This code is based on the idea of converting each digit of a decimal number into its binary equivalent in spite of converting the entire decimal value into a pure binary form. In this coding technique each decimal digit is independently converted to a  4 bit binary number which makes conversion process very easy.2⁴=16 configurations are possible but only first 10 are used to represent decimal digits from 0 to 9.

Character	BCD Code		Octal Equivalent
	Zone	Digit
A	11	0001	61
B	11	0010	62
C	11	0011	63
D	11	0100	64
E	11	0101	65
F	11	0110	66
G	11	0111	67
H	11	1000	70