Computer Architecture: Intro Lecture 8 The Control Path

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Computer Architecture IntroLecture 8- The
Control Path

• J. Schmalzel
• S. Mandayam

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Control Path

• Hard-wired control
• Sequencer
• Microprogramming (also may see Microsequencer)

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Microprogrammed Control

• A control unit w/ binary control values stored in
  microprogram memory
• This memory is local to the CPU and is not main
  memorywhere program instructions are stored

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ROM (RAM) Table Lookup

• Expensivebut highly reconfigurablemethod to
  perform combinatorial decoding/encoding functions
• Table lookup technique
• FPGA CLB

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Return to the FA

• Full Adder

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Full Adder Truth Table
Sum-of-Product Boolean expressions for S and
Co S CiAB CiAB CiAB CiAB Co
CiAB CiAB CiAB CiAB
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FA Implementation using ROM
Inputs are ROM ADDRESSES Outputs are ROM CONTENTS
(DATA)
Am-1 A2 A1 A0
Dn-1 D2 D1 D0
. .
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Example 16 x 4 ROM
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Example 16 x 4 ROM
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Things to Watch for

• Unused bits
• Dont cares

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Structure for ?P Control
NAG
CAR
ROM
CDR
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Questions, Comments, Discussion