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Why is the Op-code the first part of an instruction loaded into the instruction register of the CPU?
CaoimheG
Not necessarily. Some processors (Z80, for example) allow "prefixes" before the op-code.
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What does if statements in c plus plus implement?
C++ if() statements implements a comparison and a jump opcode. By way of example, consider the following code:if( x 100 ) generates a compare and jump opcode (cmp and jne).The cmp opcode compares the value of x with 64h (100 decimal) which will either set or clear ZF (the zero flag). If x is 100, then ZF will be unset, otherwise it will be set.The jne (jump if not equal) opcode tests ZF. If it is set, then x was not 100 and the operand (1181934h) is passed to the PC register (the program counter). The IR (instruction register) will fetch the value from PC on the next cycle. This ultimately causes execution to jump to the statement immediately following the else clause of the if statement (the second printf statement).If ZF is not set, then x really was 100 and the PC register remains unaffected. At that point the PC register will contain the value 0118191Bh, which is the next instruction after the if statement, thus execution simply falls through to the first printf statement. After processing the printfinstructions, execution will reach the else clause which simply forces a jump to bypass the second printfstatement.Thus, one of the printf statements is executed and then execution continues from the instruction at 118194Bh, which is not shown but is the next instruction after the second printfstatement.
What is the difference between register and resister in elecronics?
A resistor reduces the flow of current between two terminals and thus reduces voltage. this is achieved through electrical resistance. All electrical conductors are resisters, some more resistant than others. The less resistance offered by a conductor, the easier it is for electricity to flow, thus the higher the current. Thus resisters allow circuit designers to control the flow of electricity. A register is a small unit of storage used by a digital processor. Computers typically have a relatively large array of working memory, however all the actual processing is done via a small set of registers. Registers work in much the same way as main memory, typically using a capacitor and transistor pair to denote each bit, however registers are significantly faster. Some registers are used for housekeeping purposes such as to keep track of the next instruction and for marking the top of the program stack, while other are used to provide input and output for the current instruction. In order for an instruction to process a value that value must first be moved to a register, typically one of the accumulator registers. If the instruction requires another operand, it must be moved to another register, typically a user register. After processing, the accumulator's value is moved back to main memory, either by the instruction itself or by a subsequent instruction.
How does the CPU differentiate between command and data?
In general the only difference between commands, or instructions, and data is the context in which each appears. If the CPU is fetching the contents of memory to get the next instruction, then it assumes that the Program Counter register points to commands. If the CPU is executing an instruction that needs to fetch data from memory, the data at the address specified by the instruction are fetched, assuming that the address points to data. This is what allows a program to be loaded into memory in the first place; the part of the operation system responsible for this operation treats the program as data, loading it into memory as instructed in the file. Then the OS branches to a specified place within that memory and begins fetching instructions there. This blurring between instructions and data has also been used in the past to allow a program to modify itself as it executes. This is usually considered poor practice; some operating systems, such as HP's OpenVMS, even set up memory page protections to keep this from happening.
What does BASIC as in the programming language stand for?
Beginners All-purpose Symbolic Instruction Code > B.A.S.I.C. > Basic. John Kemeny and Thomas Kurtz developed the first version at Dartmouth University in 1964. It was originally created to allow non technical people to run a computer because, at that time, you couldn't operate a computer without programming it first. Basic was developed to give a more simple programming structure that was close to plain English so that anyone could use a computer. It has come a very long way since then becoming a very robust language.
How many machine cycles do one byte instructions have?
Depending on the particular microprocessor, a machine cycle is the fetch or store of one (typically, one byte) native word. In the 8085, this is a byte fetch or store, plus the overhead in decoding and processing the instruction. In this case, the first machine cycle is four clock cycles, or T states, and subsequent machine cycles are three clock cycles, although certain instruction sequences, such as DAD, require two extra clock cycles.
What are operands?
Every instruction contains to parts: operation code[opcode],and operand. The first part of an instruction which specifies the task to be performed by the computer is called opcode. The second part of the instruction is the data to be operated on.,and it is called operand. The operand[or data]given in the instruction may be in various forms such as 8-bit or 16-bit data, 8-bit or 16-bit address, internal register or a register or memory location.
What the Difference between accumulator and register?
The accumulator is a general register that holds a value. It is also a special register that can be used as the target for the result of various arithmetic or logical computations. For instance, if you wanted to add two numbers, you could load the first into the accumulator, add the second to the accumulator, and then store the accumulator where wanted. The instruction register is an internal register that holds the value of the instruction opcode in order for the 8085 to decode and process the instruction. While it is shown on the Intel block diagram for the 8085, it is not directly accessible by the running program - it is for internal use only by the 8085.
How does microprocessor differentiate between data and instruction code?
i) Instruction code deals only with mnemonics and its corresponding opcode but data code refers to your data like 10h which is always of 8 bits or a particular address say 8080h which is of 16 bits. ii) Data is your input to the instruction but an opcode is native to your machine. iii) Data is user specific instruction while opcode is machine specific instruction iv) You can alter data code but you cannot modify an instruction opcode.
What the Difference between accumulator and instruction register?
Examples: /360: no accumulator 8080: A 6800: A and B 8086: AX ...
What is 3 byte instruction in microprocessor?
A two-byte instruction gives the specific function instruction in two bytes, or two words. The first specifies the opcode, which tells the microprocessor what operation will occur. The second specifies the operand, or the data that the operation is done on.
How does the microprocessor work?
Suppose we give a 8-bit instruction ADD B to the microprocessor then this instruction is not at all understood by microprocessor as it only accepts binary inputs so first of all it stores the instruction in the INSTRUCTION REGISTOR then it decodes this instruction ADD B to its suitable binary code 80H in the INSTRUCTION DECODER.. after converting to 80H then the microprocessor understands that .. yes i have to add the content of the resistor B with that of A(accumulator) and store the result in the accumulator A this is a small example how microprocessor operates facing the instructions
Why 8085 microprocesseor cannot have more than 256 instruction?
Intel designed the 8085 as a 8 bit computer, with the opcode byte as the first byte of the instruction. As such, there are only 256 possible values for the first opcode byte. (28 = 256) As implemented, Intel provided only 83 different instructions.It is possible, however, in general, that secondary opcode space be usable, so the "8 bit" rule might not necessarily apply, but Intel chose to not implement any of them on the 8085, like they did on the 8086/8088.
How does the CPU keep track of which instruction to execute next?
The instruction register holds a pointer to the current instruction (in working memory) while the next instruction register points to the next instruction (the first instruction immediately after the current instruction's operands). If the current instruction is a jump instruction, it can change the next instruction register, allowing the program to branch to a new instruction once the jump instruction is processed. The next instruction pointer is automatically moved into the current instruction register once the current instruction has been processed. The entire process of executing an instruction is known as the fetch-decode-execute cycle.
What is the advantage of using sjmp over ljmp?
SJMP is short jump. In this 2-byte instruction the first byte is opcode and second byte is relative address of target location. This can save some byte of memory in many applications where memory space is in short supply where as LJMP (Long Jump) is 3-byte instruction in which 1st byte is opcode and 2nd and 3rd byte represent the 16- bit address of target location.
What is the offset at which the first executable instruction of a COM file must be placed?
What is the offset at which the first executable instruction of a COM file must be placed? The very first instruction in our assembly programs i.e. [org 0x0100] tell that its .com file shall be loaded at an offset address 100 in the segment. This is done to maintain backward compatibility.
Name the part of the computer that stores all information and software?
The Hard Drive is the main storage unit in a normal, desktop computer. This is the only internal component in a standard computer that has information when the machine is turned off (all your saved files, the operating system (such as Windows), etc). There are other components (such as RAM, or Random Access Memory) that store data, but this usually serves a special purpose, or is only at run-time.
What does if statements in c plus plus implement?
C++ if() statements implements a comparison and a jump opcode. By way of example, consider the following code:if( x 100 ) generates a compare and jump opcode (cmp and jne).The cmp opcode compares the value of x with 64h (100 decimal) which will either set or clear ZF (the zero flag). If x is 100, then ZF will be unset, otherwise it will be set.The jne (jump if not equal) opcode tests ZF. If it is set, then x was not 100 and the operand (1181934h) is passed to the PC register (the program counter). The IR (instruction register) will fetch the value from PC on the next cycle. This ultimately causes execution to jump to the statement immediately following the else clause of the if statement (the second printf statement).If ZF is not set, then x really was 100 and the PC register remains unaffected. At that point the PC register will contain the value 0118191Bh, which is the next instruction after the if statement, thus execution simply falls through to the first printf statement. After processing the printfinstructions, execution will reach the else clause which simply forces a jump to bypass the second printfstatement.Thus, one of the printf statements is executed and then execution continues from the instruction at 118194Bh, which is not shown but is the next instruction after the second printfstatement.
