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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: IntroLecture 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 • This memory is local to the CPU and is not main memory—where program instructions are stored
ROM (RAM) Table Lookup • Expensive—but highly reconfigurable—method to perform combinatorial decoding/encoding functions • Table lookup technique • FPGA CLB
A S B FA Ci Co Return to the FA • Full Adder
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
FA Implementation using ROM Inputs are ROM ADDRESSES Outputs are ROM CONTENTS (DATA) Am-1 A2 A1 A0 Dn-1 D2 D1 D0 . .
Things to Watch for… • Unused bits • Don’t cares
Structure for P Control: NAG CAR ROM CDR