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Unformatted text preview: Lecture 14 – 10/1/10 • Announcements – Come see me if you are not doing well in the class! • Last Week (P&P 4-5) – Von-Neumann Model – LC-3 Computational & Memory Instructions • This Week (P&P 5, 9.1-2) – Test #1 – LC-3 Control Instructions – TRAP and JSR instructions (covered in P&P 9.1-9.2) • Next Week – LC-3 Program Execution CS310 Fall 2010 - Boral Control Instructions • Alter the sequence of instructions – By changing the PC • Three flavors in LC-3 – Conditional branches • May be taken • PC-relative addressing – Unconditional jumps • Always taken – TRAPs • Calls to the OS for service • Upon completion of service control is returned to the instruction that immediately follows the TRAP CS310 Fall 2010 - Boral Condition Codes • N, Z, P registers – 1-bit wide – Exactly one is set to “1” the other to “0” as a side effect by any instruction that writes a value to a register • ADD, AND, NOT, LD, LDR, LDI, LEA • Used by conditional branch instruction to determine whether the branch should be taken • Other ways to do conditional branches possible – Direct instructions CS310 Fall 2010 - Boral Branch Instruction • Several variants – Specifies condition code (n, z, p) – Branch taken if corresponding Condition Code Register is on – BRp, BRn, BRz, BRnz, BRnp, BRzp, BRnzp, BR – Opcode is the same in all cases (0000) • PC-relative addressing used to compute target address...
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This note was uploaded on 11/30/2010 for the course CS 310 taught by Professor Fussell during the Spring '08 term at University of Texas.
- Spring '08