We wish to execute a single LC-3 instruction that will subtract the decimal number 25 from register 1 and put the result in register 2. Can we do it, if yes, show how it would be done, if not, explain why not

Question

Nico Holland

Engineering

17 December, 23:06

We wish to execute a single LC-3 instruction that will subtract the decimal number 25 from register 1 and put the result in register 2. Can we do it, if yes, show how it would be done, if not, explain why not

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Answers (1)

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Nelson Walsh · Answer 1

No

Explanation:

Brief introduction to lc-3

The LC-3 defines a word size of 16 bits for its registers. It also utilizes a 16 bit addressable memory with 216 location address space. The register file has 8 registers (R0 - R7), and all its registers are referred to as general-purpose registers because they can be freely used by any of the instructions that is enabled to write to the register file.

No, it is not possible to use a single LC-3 instruction to implement the subtraction operation, because we only have a 5-bit 2's complement immediate value which can only be used to represent values between - 16 and 15