INSTRUCTION CODESAND
COMPUTER REGISTERS
Nikhil Gaba
8125
Instruction code An instruction code is a group of bits that
instruct the computer to perform a specific operation.
Two parts-
Operation code-specifies the operation
Address-specifies operands, registers or memory word
Stored program organization
Direct and Indirect address
When the second part of an instruction code specifies the actual operand instruction is said to have an immediate operand.
When the second part specifies the address of operand it is called direct address.
When the second part specifies the address of the memory word in which address of the operand is found is called indirect address.
Basic computer registers
Functions
DR-Holds memory operand AC-Processor register IR-Holds instruction code TR-Holds temporary data AR-Holds address for memory PC-Hold address of next instruction INPR-Holds input character OUTR-Holds output character
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