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Computer Architecture: Intro Lecture 8- The Control Path

Computer Architecture: Intro Lecture 8- The Control Path. J. Schmalzel S. Mandayam. Control Path. Hard-wired control Sequencer Microprogramming (also may see “Microsequencer”). Microprogrammed Control. A control unit w/ binary control values stored in microprogram memory

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Computer Architecture: Intro Lecture 8- The Control Path

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  1. Computer Architecture: IntroLecture 8- The Control Path J. Schmalzel S. Mandayam

  2. Control Path • Hard-wired control • Sequencer • Microprogramming (also may see “Microsequencer”)

  3. Microprogrammed Control • A control unit w/ binary control values stored in microprogram memory • This memory is local to the CPU and is not main memory—where program instructions are stored

  4. ROM (RAM) Table Lookup • Expensive—but highly reconfigurable—method to perform combinatorial decoding/encoding functions • Table lookup technique • FPGA CLB

  5. A S B FA Ci Co Return to the FA • Full Adder

  6. Ci A B S Co 0 0 0 0 0 0 0 1 1 0 0 1 0 1 0 0 1 1 0 1 1 0 0 1 0 1 0 1 0 1 1 1 0 0 1 1 1 1 1 1 Full Adder Truth Table Sum-of-Product Boolean expressions for S and Co: S = Ci*A*B + Ci*AB* + CiA*B* + CiAB Co = Ci*AB + CiA*B + CiAB* + CiAB

  7. FA Implementation using ROM Inputs are ROM ADDRESSES Outputs are ROM CONTENTS (DATA) Am-1 A2 A1 A0 Dn-1 D2 D1 D0 . .

  8. Example 16 x 4 ROM

  9. Example 16 x 4 ROM

  10. Things to Watch for… • Unused bits • Don’t cares

  11. Structure for P Control: NAG CAR ROM CDR

  12. Questions, Comments, Discussion

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