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DMA represents Direct Memory Access. It is a hardware-controlled data transfer technique. An external device is used to control data transfer. The external device generates address and control signals that are required to control data transfer. External devices also allow peripheral devices to directly access memory. The external device which controls the data transfer is called the DMA controller.DMA Idle CycleWhen the system is turned on, the switches are in position A. The processor starts implementing the program until it requires to read a block of information from the disk. The disk processor transfers a sequence of commands to the ... Read More
An interrupt I/O is a process of data transfer in which an external device or a peripheral informs the CPU that it is ready for communication and requests the attention of the CPU.I/O ConfigurationThe terminals send and receive serial information. Each portion of serial data has eight bits of alphanumeric code, where the leftmost bit is continually 0. The serial data from the input register is transferred into the input register INPR. The output register OUTR can save the serial data for the printer. These two registers interact with the Accumulator (AC) in parallel and with a communication interface in ... Read More
In multilevel interrupts, more than one interrupt pin is present in the processor. Hence, interrupts can be recognized by the CPU on getting an interrupt request from some of the interrupt pins.The figure shows the multilevel interrupt system.Let us now discuss the process flow of a multilevel interrupt. When the external asynchronous input is inserted, the logic control of a multilevel interrupt is as follows −The processor completes its current instruction.The current contents of the program counter are stored in the stack.The program counter is loaded with the address of an interrupt service routine.Program execution reaches with the instruction taken ... Read More
In single level interrupts, many devices can interrupt the processor at the same time to attend to their requests. But all the devices raise requests through a single input pin of the CPU. When interrupted, the CPU must identify the device that raised the request. Once the I/O port is identified, the CPU attends to the request of I/O device and then continues to carry out the task that it was performing before being interrupted.In single-level interrupts, interrupt requests from all the devices are logically ORed and connected to the interrupt input of the processor. Hence, the interrupt request from ... Read More
In data transfer schemes, it can provide an efficient means of transmitting data between the processing unit and the I/O devices. In a computer, the data transfer happens between any of these combinations CPU and memory, CPU and I/O devices, and memory and I/O devices.A computer is interfaced with many devices of different speeds. Therefore, I/O devices may not be ready to transfer data as soon as the microprocessor issues the instruction for this purpose. Many data transfer schemes have been developed to solve this problem.Classification of Data Transfer SchemesThe data transfer schemes have been broadly classified into two categories ... Read More
ASCII represents American Standard Code for Information Interchange. It is the standard binary code used to represent alphanumeric characters. Alphanumeric characters are used for the transfer of information to and from the I/O devices and the computer. This standard helps seven bits to code 128 characters. However, there is an additional bit on the left that is always assigned 0. Therefore, there are 8 bits in total.The ASCII code consists of 34 nonprinting characters and 94 characters used for various control operations. There are 26 uppercase letters A through Z, 26 lowercase letters a through z, numerals from 0 to ... Read More
The Booth multiplication algorithm defines a multiplication algorithm that can multiply two signed binary numbers in two’s complement. This algorithm helps in the study of computer architecture.Booth’s algorithm contains the addition of one of two predetermined values (A and S) to a product (P) continually and then implementing a rightward arithmetic shift on the product (P). Let us consider the predetermined values to be A and S, and the product to be P. Consider that the multiplicand and multiplier are m and r respectively. Let the number of bits in m and r be x and y respectively.The Booth’s multiplication ... Read More
An algorithm to multiply two numbers is known as the multiplication algorithm. The hardware multiply algorithm is used in digital electronics such as computers to multiply binary digits. The figure shows the flowchart for the hardware multiply algorithm.In the flowchart shown in the figure, the multiplicand is in Y and the multiplier is in Q. The signs related to Y8 and Q8 are in respectively. These signs are compared and both X and Q are set to correspond to the sign of the product because a double-length product will be stored in registers X and Q.The registers X and E ... Read More
Binary numbers are subtracted by performing two’s complement on the subtrahend. Two’s complement is done through the following steps −Complement every digit. That is, change 1 to 0 and 0 to 1.Add 1 to the output.The following example illustrates the subtraction operation of binary digits using the above-mentioned steps.Example: 11101011 - 01100110The second value 01100110 is to be subtracted from the first value 11101011.First apply two’s complement to the second value 01100110, i.e., follow the two steps as shown.Step 1: 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 (change 1 to 0 ... Read More
The addition of binary numbers is easy yet tedious at the same time. It is a fundamental feature of digital computers, and hence it is important to know how to add binary digits.Almost all the operations of a computer depend on binary addition. Once we understand the addition of two binary digits, it is easier to understand subtraction, multiplication, and division of binary digits.We can start by adding two binary bits. As you are aware a bit can be either 0 or 1. Therefore, we can have only four possible input combinations. The four possible input combinations and their output ... Read More