Indirect Addressing second part of instruction designates an address of a

Indirect addressing second part of instruction

This preview shows page 6 - 13 out of 49 pages.

Indirect Addressing : second part of instruction designates an address of a memory in which the address of the operand is found Opcode Address Instruction Format 15 14 12 0 I 11 Addressing mode
Image of page 6

Subscribe to view the full document.

Basic Computer Organization and Design 7 CSE 211 Addressing Mode The address field of an instruction can represent either Direct address : the address in memory of the data to use (the address of the operand), or Indirect address : the address in memory of the address in memory of the data to use Effective Address (EA) The address, that can be directly used without modification to access an operand for a computation-type instruction, or as the target address for a branch-type instruction 0 ADD 457 22 Operand 457 1 ADD 300 35 1350 300 Operand 1350 + AC + AC Direct addressing Indirect addressing
Image of page 7
Basic Computer Organization and Design 8 CSE 211 Processor Register A processor has many registers to hold instructions, addresses, data, etc The processor has a register, the Program Counter (PC) that holds the memory address of the next instruction to be executed Since the memory in the Basic Computer only has 4096 locations, the PC only needs 12 bits In a direct or indirect addressing, the processor needs to keep track of what locations in memory it is addressing: The Address Register (AR) is used for this The AR is a 12 bit register in the Basic Computer When an operand is found, using either direct or indirect addressing, it is placed in the Data Register (DR) . The processor then uses this value as data for its operation The Basic Computer has a single general purpose register – the Accumulator (AC)
Image of page 8

Subscribe to view the full document.

Basic Computer Organisation and Design 9 CSE 211 Processor Register The significance of a general purpose register is that it can be referred to in instructions e.g. load AC with the contents of a specific memory location; store the contents of AC into a specified memory location Often a processor will need a scratch register to store intermediate results or other temporary data; in the Basic Computer this is the Temporary Register (TR) The Basic Computer uses a very simple model of input/output (I/O) operations Input devices are considered to send 8 bits of character data to the processor The processor can send 8 bits of character data to output devices The Input Register (INPR) holds an 8 bit character gotten from an input device The Output Register (OUTR) holds an 8 bit character to be send to an output device
Image of page 9
Image of page 10

Subscribe to view the full document.

Basic Computer Organization and Design 11 CSE 211 Processor Register List of BC Registers DR 16 Data Register Holds memory operand AR 12 Address Register Holds address for memory AC 16 Accumulator Processor register IR 16 Instruction Register Holds instruction code PC 12 Program Counter Holds address of instruction TR 16 Temporary Register Holds temporary data INPR 8 Input Register Holds input character OUTR 8 Output Register Holds output character Registers in the Basic Computer 11 0 PC 15 0 IR 15 0 TR 7 0 OUTR 15 0 DR 15 0 AC 11 0 AR INPR 0 7 Memory 4096 x 16 CPU
Image of page 11
Basic Computer Organization and Design 12
Image of page 12

Subscribe to view the full document.

Image of page 13
  • Summer '17

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Ask Expert Tutors You can ask 0 bonus questions You can ask 0 questions (0 expire soon) You can ask 0 questions (will expire )
Answers in as fast as 15 minutes