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Overview

Overview. The Operate Instructions - ADD, AND, NOT The Data Movement Instructions - Load, Load Address, Store Example Using Operate & Data Movement The Control instructions - BR, JMP, TRAP. Example. Opcode. Branch Instruction. BR [0000 nzp PCoffset9]

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Overview

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Presentation Transcript

  1. Overview The Operate Instructions - ADD, AND, NOT The Data Movement Instructions - Load, Load Address, Store Example Using Operate & Data Movement The Control instructions - BR, JMP, TRAP

  2. Example Opcode

  3. Branch Instruction BR [0000 nzp PCoffset9] • Branch specifies one or more condition codes • If the set bit is specified, the branch is taken: • PC is set to the address specified in the instruction • Target address is made by adding SEXT(IR[8:0]) to the PC • If the branch is not taken: - the next sequential instruction (PC) is executed.

  4. BR ///////////// ///// + SEXT

  5. Jump Instruction JMP BaseR [1100 000 BaseR 000000] • Jump is an unconditional branch -- always taken. • Base • Address is contents of the register • Allows any target address.

  6. TRAP • Calls a service routine, identified by 8-bit “trap vector.” • When routine is done, PC is set to the instruction following TRAP.

  7. LC-3 Memory Map

  8. TRAPS

  9. Using Branch Instructions • Compute sum of 12 integers.Numbers start at location x3100. Program starts at location x3000. R1  x3100R3  0R2  12 R2=0? R4  M[R1]R3  R3+R4R1  R1+1 R2  R2-1 NO YES

  10. Sample Program

  11. clear R2 add R4 to R2 decrement R5 R5 = 0? No Yes HALT Example 1: Multiply • This program multiplies two unsigned integers in R4 and R5. x3200 0101010010100000 x3201 0001010010000100 x3202 0001101101111111 x3203 0000011111111101 x3204 1111000000100101 R2 <- 0 R2 <- R2 + R4 R5 <- R5 – 1 BRzp x3201 HALT

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