Hardware Implementation - selective set




The selective-set operation sets to 1 the bits in register A where there are corresponding 1's in register B. It does not affect bit positions that have D's in B. The following numerical example clarifies this operation.

            1010 A before

            1100 B (logic operand)

            1110 A after

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The two leftmost bits of B are 1' s, so the corresponding bits of A are set to 1. One of these two bits was already set and the other has been changed from 0 to I. The two bits of A with corresponding 0' s in B remain unchanged. The example above serves as a truth table since it has all four possible combinations of two binary variables. From the truth table we note that the bits of A after the operation are obtained from the logic-OR operation of bits in B and previous values of A. Therefore, the OR rnicrooperation can be used to selectively set bits of a register.

selective-complement: The selective-complement operation complements bits in A where there are selective-clear corresponding l's in B. It does not affect bit positions that have D's in B. For example

                           1010 A before

                           1100 B (logic operand)

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                           0110 A after

Again the two leftmost bits of B are 1's, so the corresponding bits of A are complemented. This example again can serve as a truth table from which one can deduce that the selective-complement operation is just an exclusive-OR rnicrooperation. Therefore, the exclusive-OR rnicrooperation can be used to selectively complement bits of a register.

 



Frequently Asked Questions

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Ans: Logic microoperations are very useful for manipulating individual bits or a portion of a word stored in a register. They can be used to change bit values, delete a group of bits, or insert new bit values into a register. view more..
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Ans: The hardware implementation of logic rnicrooperations requires that logic gates be inserted for each bit or pair of bits in the registers to perform the required logic function. Although there are 16 logic rnicrooperations, most computers use only four-AND, OR, XOR (exclusive-OR), and complementfrom which all others can be derived. view more..
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Ans: There are 16 different logic operations that can be performed with two binary variables. They can be determined from all possible truth tables obtained with two binary variables as shown in Table 4-5. In this table, each of the 16 columns F0 through F15 represents a truth table of one possible Boolean function for the view more..
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Ans: The selective-set operation sets to 1 the bits in register A where there are corresponding 1's in register B. It does not affect bit positions that have D's in B. The following numerical example clarifies this operation. view more..
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Ans: Shift rnicrooperations are used for serial transfer of data. They are also used in conjunction with arithmetic, logic, and other data-processing operations. The contents of a register can be shifted to the left or the right. At the same time that the bits are shifted, the first flip-flop receives its binary information from the serial input view more..
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Ans: Instead of having individual registers performing the microoperations directly, computer systems employ a number of storage registers connected to a common operational unit called an arithmetic logic unit, abbreviated ALU. view more..
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Ans: In this chapter we introduce a basic computer and show how its operation can be puter specified with register is defined by its internal transfer registers, statements. the limirlg The otganization and control of structure, the comand the set of instructions that It uses. The design of the computer is then carried out in detall. Although the basic computer presented in this chap view more..
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Ans: An instruction code is a group of bits that instruct the computer to perform a specific operation. It is usually divided into parts, each having its own particular interpretation. The most basic part of an instruction code is its operation part. The operation code of an instruction is a group of bits that define such operations as add, view more..
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Ans: The simplest way to organize a computer is to have one processor register and an instruction code format with two parts. The first part specifies the operation to be performed and the second specifies an address. The memory address tells the control where to find an operand in memory. This operand is read from memory and used as the data to be operated on together with the data stored in the processor register view more..
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Ans: In this chapter we introduce a basic computer and show how its operation can be puter specified with register is defined by its internal transfer registers, statements. the limirlg The otganization and control of structure, the comand the set of instructions that It uses. The design of the computer is then carried out in detall. Although the basic computer presented in this chapter is very small compared to commercial computers, It has the advantage of being simple enough so we can demonstrate the design process without too many complications. view more..
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Ans: It is sometimes convenient to use the address bits of an instruction code not as an address but as the actual operand. When the second part of an instruction code specifies an operand, the instruction is said to have an immediate operand. view more..
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Ans: Computer instructions are normally stored in consecutive memory locations and are executed sequentially one at a time. The control reads an instruction from a specific address in memory and executes it. It then continues by reading the next instruction in sequence and executes it, and so on. view more..
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Ans: The memory address register (AR) has 12 bits since this is the width of a memory address. The program counter (PC) also has 12 bits and it holds the address of the next instruction to be read from memory after the current instruction is executed. The PC goes through a counting sequence and causes the computer to read sequential instructions previously stored in memory. Instruction words are read and executed in sequence unless a branch instruction is encountered. view more..
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Ans: The basic computer has eight registers, a memory unit, and a control unit. Paths must be provided to transfer information from one register to another and between memory and registers. view more..
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Ans: The input data and output data of the memory are connected to the common bus, but the memory address is connected to AR. Therefore, AR must always be used to specify a memory address. By using a single register for the address, we eliminate the need for an address bus that would have been needed otherwise. The content of any register can be specified for the memory data input during a write operation. Similarly, any register can receive the data from memory after a read operation except AC . view more..
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Ans: The basic computer has three instruction code formats, as shown in Fig. 5-5. Each format has 16 bits. The operation code (opcode) part of the instruction contains three bits and the meaning of the remaining 13 bits depends on the operation code encountered. view more..
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Ans: Before investigating the operations performed by the instructions, let us discuss the type of instructions that must be included in a computer. A computer should have a set of instructions so that the user can construct machine language programs to evaluate any function that is known to be computable. The set of instructions are said to be complete if the computer includes a sufficient number of instructions in each of the following categories: view more..
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Ans: The timing for all registers in the basic computer is controlled by a master clock generator. The clock pulses are applied to all flip-flops and registers in the system, including the flip-flops and registers in the control unit. The clock pulses do not change the state of a register unless the register is enabled by view more..




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