What is Signals and Number Systems

 1. Analog Signals An analog signal is a signal whose amplitude is a function of time and changes gradually as time changes. Analog signals can be classified as non periodic and periodic signals.

2. Non periodic Signal In a non periodic signal, there is no repeated pattern in the signal

3. Periodic Signal A signal that repeats a pattern within a measurable time period is called a periodic signal, and completion of a full pattern is called a cycle.

4. Digital Signals Modern computers communicate by using digital signals. Digital signals are represented by two voltages: one voltage represents the number 0 in binary, and the other voltage represents the number 1 in binary. where 0 volts represents 0 in binary and þ5 volts represents 0 or 1 is called a bit and 8 bits is called a byte.

Unsigned, Signed Magnitude, and Signed Two’s Complement Binary Number

A binary number can be represented in form unsigned number or signed number or  signed two’s complement, þ sign represented by 0 and – sign represented by 1.

Unsigned Number In an unsigned number, all bits of a number are used to represent the number, but in a signed number, the most significant bit of the number represents the sign. A 1 in the most significant position of number represents a negative sign, and 0 in the most significant position of number represents a positive sign. The 1101 unsigned value is 13.

Signed Magnitude Number In a signed number, the most significant bit represents the sign, where 1101 ¼ _5 or 0101 ¼ þ5 In unsigned number, 1101 ¼ 13.

Signed Two’s Complement A signed two’s complement applies to a negative number. If the sign of the number is one, then the number is represented by signed two’s complement.

 Parity Bit

A parity bit is used for error detection of information, since a bit or bits may be changed during the transmission of information from source to destination, a parity bit is an extra bit appended to the information. It represents whether the number of ones or zeroes is either even or odd in the original transmission and can alert the destination to a loss of information.

Even Parity: The extra bit (0 or 1) is chosen such that the number of ones becomes even.

 Odd Parity: The extra bit (0 or 1) is chosen such that the number of ones becomes odd.

 Transmission Modes

When data is transferred from one computer to another by digital signals, the receiving computer has to distinguish the size of each signal to determine when a signal ends and when the next one begins. Synchronization methods between source and destination devices are generally grouped into two categories: asynchronous and synchronous.

 Asynchronous Transmission

 Asynchronous transmission occurs character by character and is used for serial communication, such as by a modem or serial printer. In asynchronous transmission, each data character has a start bit which identifies the start of the character and 1 or 2 bits which identifies the end of the character. The data character is 7 bits. Following the data bits may be a parity bit, which is used by the receiver for error detection. After the parity bit is sent, the signal must return to high for at least 1 bit time to identify the end of the character. The new start bit serves as an indicator to the receiving device that a data character is coming and allows the receiving side to synchronize its clock. Since the receiver and transmitter clock are not synchronized continuously, the transmitter uses the start bit to reset the receiver clock so that it matches the transmitter clock. Also, the receiver is already programmed for the number of bits in each character sent by the transmitter.

 Synchronous Transmission

Some applications require transferring large blocks of data, such as a file from disk or transferring information from a computer to a printer. Synchronous transmission is an efficient method of transferring large blocks of data by using time intervals for synchronization.