1. Computer Architecture: Intro Lecture 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. Return to the FA §Full Adder FA A B Ci S Co

6. Full Adder Truth Table 0 0 00 0 Ci A BS Co 0 0 11 0 0 1 01 0 0 1 10 1 1 0 01 0 1 0 10 1 1 1 00 1 1 1 11 1 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).... A m-1 A2 A1 A0 D n-1 D2 D1 D0

8. Example 16 x 4 ROM Add A2:Ci, A1:A, A0: B D3 (S)D2 (Co)D1D0 0 1 2 3 4 5 6 7 8 9 A B C D E F

9. Example 16 x 4 ROM Add A2:Ci, A1:A, A0: B D3 (S)D2 (Co)D1D0 000XX 110XX 210XX 301XX 410XX 501XX 601XX 711XX 800XX 910XX A10XX B01XX C10XX D01XX E01XX F11XX

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

11. Structure for  P Control: NAGCARROMCDR

12. Questions, Comments, Discussion