Dale - Computer Science Illuminated 221

Dale Computer - 194 Chapter 7 Low-Level Programming Languages Figure 7.4 Subset of Pep/7 instructions Opcode XXXXX XXXX= XXX=X XXX= XX=XX =X= =XX

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194 Chapter 7 Low-Level Programming Languages Figure 7.4 Subset of Pep/7 instructions 11111 11110 11101 11100 11011 00100 00011 Stop execution Opcode Meaning of Instruction Load operand into a register (either A of X) Store the contents of register (either A or X) into operand Add the operand to register (either A or X) Subtract the operand from register (either A or X) Character input to operand Character output from operand Instructions that do not have an operand (data to be manipulated) are called unary instructions , and do not have an operand specifier. That is, unary instructions are only one byte long rather than three bytes long. Some Sample Instructions Let’s look at some specific instructions in isolation and then put them together to write a program. Figure 7.4 contains the 5-bit operation code (or opcode ). Recall that the operation code is in the leftmost 5 bits of the instruction specifier, the 6th bit specifies the register used (if any), and address mode specifier is in the remaining 2 bits. 11111
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This note was uploaded on 01/13/2011 for the course CSE 1550 taught by Professor Marianakant during the Fall '10 term at York University.

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