#158 The hypothetical machine of Figure

The hypothetical machine of Figure - Computer Science

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The hypothetical machine of Figure 3.4 also has two I/O instructions:
0011 = Load AC from I/O
0111 = Store AC to I/O
In these cases, the 12-bit address identifies a particular I/O device. Show the program execution (using the format of Figure 3.5) for the following program:

1. Load AC from device 5.

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2.  Add contents of memory location 940.

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3.  Store AC to device 6.
Assume that the next value retrieved fromdevice 5 is 3 and that location 940 contains a value of 2.

Example of Program Execution (contents of memory and registers in hexadecimal)

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Free Chegg Answer

Program execution as per figure 3.5 from textbook:
Step 1: Instruction Register (IR)  3005.
Step 2: Accumulator (AC) 3
Step 3: Instruction Register (IR)  5940
Step 4: Accumulator (AC)  5 (3 +2)
Step 5: Instruction Register (IR)  7006
Step 6: Device 6  Accumulator (AC)

Explanation:
• Instruction register (IR) is the one which stores instruction currently being executed or decoded.
• Program counter (PC) is the one that holds address of the instruction being executed at current time.
• 12 bits is used to specify the address and 4 bits in the IR indicates accumulator to be loaded.
Let the contents of memory location be,
• 300 : 3005
• 301 : 5940
• 302 : 7006

Step 1:
In step1 the “Program Counter” holds the value of “300” and “Instruction register” holds contents of address “300” that is “3005”.

Step 2 & Step 3:
The content of address location “005” is moved to the accumulator and Instruction register holds the value “5940

Step 4:
Add contents of Accumulator with contents of address “940” and stored back to accumulator.

Step 5:
The next instruction (7006) is fetched from location 302 and PC is incremented.

Step 6:
The contents of the AC are stored in location 006

Thus, execution steps for the given problem according to figure 3.5 from text book is done.