Basic Operational Concepts The computer works based on some
given instruction. Let us consider an
example: Add LOCA, R0 -> This instruction adds the operands at
memory location LOCA to the operand in
the register R0 and places the sum into
the register R0.It seems that this
instruction is done in one step, but
actually it internally performs several steps ->First, the instruction is fetched from the
memory into the processor. Next, the
operand at LOCA is fetched and added to
the contents of R0. The above instruction can be written also
as- Load LOCA, R1 Add R1,R0 LET US NOW ANALYSE HOW THE MEMORY AND PROCESSOR ARE CONNECTED:- The Processor contains a number of
registers used for several purposes. IR: The IR(Instruction Register) holds
the instruction that is currently being
executed. PC: The PC(Program Counter) is another
specialized register which contains the
memory address of next instruction to
be fetched. MAR: This register facilitates
communication with the memory. The
MAR holds the address of the location
to be accessed. MDR: This register facilitates
communication with the memory. The
MDR contains the data to be written
into or read out of the addressed
location. There are n general purpose registers
R0 to Rn-1. The Program execution starts when the
PC is set to point the 1st instruction.
The content of the PC is transferred to
the MAR and Read control signal is sent
to memory. Then the addressed word is
read out of the memory and loaded into the MDR. Next the contents of the
MDR are transferred to the IR. Then the
program is decoded, it is sent to the
ALU if it has some arithmetic or logical
calculations. The n general purpose
registers are used during this calculations to store the result. Then
the result is sent to the MDR, and its
address of location where result is
stored is sent to MAR. And then a write
cycle is initiated. Then PC is
incremented and the process continues
given instruction. Let us consider an
example: Add LOCA, R0 -> This instruction adds the operands at
memory location LOCA to the operand in
the register R0 and places the sum into
the register R0.It seems that this
instruction is done in one step, but
actually it internally performs several steps ->First, the instruction is fetched from the
memory into the processor. Next, the
operand at LOCA is fetched and added to
the contents of R0. The above instruction can be written also
as- Load LOCA, R1 Add R1,R0 LET US NOW ANALYSE HOW THE MEMORY AND PROCESSOR ARE CONNECTED:- The Processor contains a number of
registers used for several purposes. IR: The IR(Instruction Register) holds
the instruction that is currently being
executed. PC: The PC(Program Counter) is another
specialized register which contains the
memory address of next instruction to
be fetched. MAR: This register facilitates
communication with the memory. The
MAR holds the address of the location
to be accessed. MDR: This register facilitates
communication with the memory. The
MDR contains the data to be written
into or read out of the addressed
location. There are n general purpose registers
R0 to Rn-1. The Program execution starts when the
PC is set to point the 1st instruction.
The content of the PC is transferred to
the MAR and Read control signal is sent
to memory. Then the addressed word is
read out of the memory and loaded into the MDR. Next the contents of the
MDR are transferred to the IR. Then the
program is decoded, it is sent to the
ALU if it has some arithmetic or logical
calculations. The n general purpose
registers are used during this calculations to store the result. Then
the result is sent to the MDR, and its
address of location where result is
stored is sent to MAR. And then a write
cycle is initiated. Then PC is
incremented and the process continues
