SCRAM Instructions Philipp Koehn 16 September 2019 Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
Reminder 1 • Fully work through a computer – circuit – assembly code • Simple but Complete Random Access Machine (SCRAM) – every instruction is 8 bit – 4 bit for op-code: 9 different operations (of 16 possible) – 4 bit for address: 16 bytes of memory • Background reading on web page – The Random Access Machine – The SCRAM Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
Circuit (At This Point) 2 W W MAR A 16x8 RAM W PC DI DO INC W MBR W IR C D Decoder Q Control Logic Unit T NOT INC CLEAR Decoder T Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
Instruction Fetch 3 • Retrieve instruction from memory • Increase program counter Time Command MAR ← PC t 0 MBR ← M, PC ← PC + 1 t 1 IR ← MBR t 2 Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
4 lda Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
Micro Program 5 • Load into accumulator Op Code Time Command MAR ← IR(D) q 1 t 3 MBR ← M q 1 t 4 AC ← MBR q 1 t 5 Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
Accumulator 6 W W A MAR 16x8 RAM W PC DO DI INC W MBR W IR C D Decoder Q W AC Control Logic Unit T NOT INC CLEAR Decoder T Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
AC ← MBR 7 W W A MAR 16x8 RAM W PC DO DI INC W MBR W IR C D Decoder Q W AC Control Logic Unit T NOT Accumulator receives value INC CLEAR from memory buffer (MBR) Decoder T Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
MAR ← IR(D) 8 W W MAR A 16x8 RAM W PC DI DO INC W MBR W IR C D Decoder Q W AC Control Logic Unit T NOT Memory address comes from INC CLEAR data field of instruction Decoder T Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
MAR ← IR(D) 9 W W MAR A 16x8 RAM W S PC Selector DI DO INC W MBR W IR C D Decoder Q W AC Control Logic Unit T NOT Selector INC CLEAR picks between inputs Decoder T Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
10 let’s do this again but focus on flags Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
Micro Program 11 • Load into accumulator Op Code Time Command MAR ← IR(D) q 1 t 3 MBR ← M q 1 t 4 AC ← MBR q 1 t 5 Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
q 1 t 3 : MAR ← IR(D) 12 W W MAR A 16x8 RAM W S PC Selector DI DO INC W MBR W IR C D Decoder Q W AC Control Logic Unit T NOT INC CLEAR Decoder T Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
q 1 t 4 : MBR ← M 13 W W MAR A 16x8 RAM W S PC Selector DI DO INC W MBR W IR C D Decoder Q W AC Control Logic Unit T NOT INC CLEAR Decoder T Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
q 1 t 5 : AC ← MBR 14 W W MAR A 16x8 RAM W S PC Selector DI DO INC W MBR W IR C D Decoder Q W AC Control Logic Unit T NOT INC CLEAR Decoder T Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
15 control logic unit Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
Objective 16 W IR C D • Given – Instruction op code Q Decoder – Time step in micro program T Q • Output Control Logic – signals to register transfer Unit – signals to selectors T NOT INC CLEAR Decoder T Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
Example 17 • Step in micro program: q 1 t 3 MAR ← IR(D) • Needs to signal – MAR write flag set – MAR’s selector to input IR(D) W W A MAR 16x8 RAM W S PC Selector DI DO INC W IR C D Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
Add Wires to the Circuit 18 W W A MAR 16x8 RAM W PC S Selector DI DO INC W MBR W IR C D Decoder Q W AC x1 Control x2 Logic Unit T NOT INC CLEAR Decoder T Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
Inside the Control Logic Unit 19 Decoder to selectior to MAR write q1 x1 x2 t5 Decoder Micro instruction: q 1 AND t 5 : MAR ← IR(D) Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
Inside the Control Logic Unit 20 Decoder to selectior to MAR write q1 x1 x2 AND t5 Decoder Micro instruction: q 1 AND t 5 : MAR ← IR(D) Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
Inside the Control Logic Unit 21 Decoder to selectior to MAR write q1 x1 x2 OR AND t5 Decoder Micro instruction: q 1 AND t 5 : MAR ← IR(D) Set signal to MAR write flag Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
Inside the Control Logic Unit 22 Decoder to selectior to MAR write q1 x1 OR x2 OR AND t5 Decoder Micro instruction: q 1 AND t 5 : MAR ← IR(D) Set appropriate value to MAR selector Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
Inside the Control Logic Unit 23 Decoder to selectior to MAR write q1 x1 OR x2 OR AND t5 OR Decoder Micro instruction: q 1 AND t 5 : MAR ← IR(D) Increase micro program time step Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
Inside the Control Logic Unit 24 Control logic is a large matrix t 0 t 1 t 2 t 3 t 4 t 5 t 6 t 7 t 8 * * * * * * * * * q 0 * * * * * * * * * q 1 * * * * * * * * * q 2 * * * * * * * * * q 3 * * * * * * * * * q 4 * * * * * * * * * q 5 * * * * * * * * * q 6 * * * * * * * * * q 7 * * * * * * * * * q 8 Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
Inside the Control Logic Unit 25 Control logic is a large matrix t 0 t 1 t 2 t 3 t 4 t 5 t 6 t 7 t 8 * * * * * * * * * q 0 * * * * * * * * * q 1 * * * * * * * * * q 2 * * * * * * * * * q 3 * * * * * * * * * q 4 * * * * * * * * * q 5 * * * * * * * * * q 6 * * * * * * * * * q 7 * * * * * * * * * q 8 Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
Inside the Control Logic Unit 26 Control logic is a large matrix t 0 t 1 t 2 t 3 t 4 t 5 t 6 t 7 t 8 * * * * * * * * * q 0 * * * * * * * * q 1 x 1 x 2 t * * * * * * * * * q 2 * * * * * * * * * q 3 * * * * * * * * * q 4 * * * * * * * * * q 5 * * * * * * * * * q 6 * * * * * * * * * q 7 * * * * * * * * * q 8 Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
27 ldi Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
LDI: Load Indirectly 28 • Specified memory address contains address for value • Basically a pointer operation • Steps – load value of specified memory address – use that value as a memory address (second lookup) – store value from second lookup into accumulator Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
Micro Program for LDI 29 • Load indirectly into accumulator Op Code Time Command MAR ← IR(D) q 2 t 3 MBR ← M q 2 t 4 MAR ← MBR q 2 t 5 MBR ← M q 2 t 6 AC ← MBR q 2 t 7 Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
q 2 t 3 : MAR ← IR(D) 30 W W MAR A 16x8 RAM W S PC Selector DI DO INC W MBR W IR C D Decoder Q W AC Control Logic Unit T NOT INC CLEAR Decoder T Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
q 2 t 4 : MBR ← M 31 W W MAR A 16x8 RAM W S PC Selector DI DO INC W MBR W IR C D Decoder Q W AC Control Logic Unit T NOT INC CLEAR Decoder T Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
q 2 t 5 : MAR ← MBR 32 W W MAR A 16x8 RAM W S PC Selector DI DO INC W MBR W IR C D Decoder Q W AC Control Logic Unit T NOT INC CLEAR Decoder T Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
q 2 t 6 : MBR ← M 33 W W MAR A 16x8 RAM W S PC Selector DI DO INC W MBR W IR C D Decoder Q W AC Control Logic Unit T NOT INC CLEAR Decoder T Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
q 2 t 7 : AC ← MBR 34 W W MAR A 16x8 RAM W S PC Selector DI DO INC W MBR W IR C D Decoder Q W AC Control Logic Unit T NOT INC CLEAR Decoder T Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
35 sta Philipp Koehn Computer Systems Fundamentals: SCRAM Instructions 16 September 2019
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