register
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Registers are small data holding places within a computer's processor. They typically hold instructions, addresses, or data and perform fetch, decode, and execute functions. The main types of registers include memory address registers, memory data registers, index registers, general purpose registers, program counters, pointer registers, accumulator registers, stack control registers, and flag registers. Flag registers in particular contain status flags that indicate conditions like carry, zero, or overflow from executed instructions.
register
- 1. REGISTERS
- 2. What is a register? A register is one of a small set of data holding places that are part of a computer processor . A register may hold : a computer instruction a storage address or any kind of data (such as a bit sequence or individual characters)
- 3. About Registers Rarely more than 64 registers in number Small in size Typically a register is less than 64 bits in size
- 6. Performance Registers Perform : Fetch Decode Execute
- 7. Types of Registers: 1. Memory Address Register (MAR) Holds the memory addresses of data and instructions Used to access data and instructions from memory during the execution phase of an instruction It contains the copy of designated memory locations specified by the memory address register.
- 8. 2. Memory Data Register (MDR) It contains the data to be stored in the computer storage (e.g. RAM). It acts like a buffer and holds anything that is copied from the memory ready for the processor to use it. MDR hold the information before it goes to the decoder.
- 10. 3.Index Register It is used for modifying operand addresses during the run of a program.
- 11. 4. General Purpose Registers Four general-purpose registers: 1. AX 2. BX 3. CX 4. DX
- 12. Combination of two 8-bit registers which are separately accessible as AL, BL, CL, DL (the "low'' bytes) and AH, BH, CH, and DH (the "high'' bytes). For example, if AX contains the 16 bit number 1234h, then AL contains 34h and AH contains 12h.
- 13. 5. Program Counter Part of the instruction sequencer in some computers It holds the address of the memory location of the next instruction when the current instruction is executed by the microprocessor.
- 15. Pointer Registers The pointer registers are 32-bit registers. There are three categories of pointer registers: Instruction Pointer (IP) Stack Pointer (SP) Base Pointer (BP)
- 16. • Instruction Pointer (IP) The 16 bit IP register stores the offset address of the next instruction to be executed. It gives the complete address of the current instruction in the code segment.
- 17. • Stack Pointer (SP) The 16-bit SP register provides the offset value within the program stack. It refers the current position of data or address within the program stack.
- 18. • Base Pointer (BP) The 16-bit BP register mainly helps in referencing the parameter variables passed to a subroutine (set of sequence).
- 19. 6. Accumulator Register Used for storing the Results those are produced by the System. When the CPU will generate Some Results after the Processing then all the Results will be Stored into the AC Register
- 20. 7. Stack Control Register A stack represents a set of memory blocks; the data is stored in and retrieved from these blocks in an order, i.e. First In and Last Out (FILO). The Stack Control Register is used to manage the stacks in memory. The size of this register is 2 or 4 bytes.
- 21. 8. Flag Registers It is a special purpose register with size one byte or two bytes. Each bit of the flag register constitutes a flag (or alarm), such that the bit value indicates if a specified condition was encountered while executing an instruction.
- 22. Types of Flag Registers Carry Flag: If 9th bit generated then the carry flag will be 1.
- 23. Types of Flag Registers Auxiliary Carry Flag: If the 4th bit contains carry then AC is 1.
- 24. Types of Flag Registers Parity Flag: If number of ones in the bit are even then PF=1 else if number of ones in the bit are odd then PF=0.
- 25. Example
- 26. Types of Flag Registers Zero Flag: If the answer is zero then ZF=1 otherwise ZF=0.
- 27. Types of Flag Registers Overflow Flag: If the bit are in the range -128 to 127 then OF=0 else OF=1.
- 28. Types of Flag Registers Sign Flag: If MSB=1 then SF=1 else MSB=0 then SF=0.