lc3_review - e) Instruction Register (IR): It holds the...

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Last updated: 12/15/2006 ECEn/CS 224 LC-3 Review Homework Solutions 1. Describe the purpose of each of the following LC-3 architectural structures: a) Program Counter (PC): Contains the address pointing to the memory location where the next instruction to be executed is located. b) MARMUX: Selects what address will be sent to the MAR (Memory Address Register). The choices are the output from the effective address block (EAB) or a zero extended offset from the instruction register (used in TRAP instructions). c) REGFILE: The register file, which in the LC-3 is the bank of eight 16-bit registers which are used to hold values. d) SEXT: Sign extender. It takes a signed number which is less than 16 bits and extends it appropriately such that the result is the signed, 16-bit version of that number.
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Unformatted text preview: e) Instruction Register (IR): It holds the instruction word which is currently being executed. 2. Describe the function of the instruction defined by each of the following 16-bit instruction words: a) 0101001001000110 Opcode DR SR1 SR2 0 1 0 1 0 0 1 0 0 1 0 0 0 1 1 0 AND R1 R1 R6 R1 b R1 AND R6 b) 1110101001011100 Opcode DR PCoffset9 1 1 1 0 1 0 1 0 0 1 0 1 1 1 0 0 LEA R5 #92 R5 b PC + #92 c) 0100000000000000 Opcode BaseR 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 JSRR R0 Last updated: 12/15/2006 3. Summarize all the steps involved when fetching an instruction from memory. 1. Load the contents of the PC into the MAR. 2. Load the contents of the memory location into MDR. While MDR is loading, increment the PC (this could instead be done in the other steps). 3. Load the contents of the MDR into the IR....
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lc3_review - e) Instruction Register (IR): It holds the...

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