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# IR, the PC , the MAR , the MDR ,and A

### #1 G!RL Posted 17 March 2005 - 11:13 PM

G!RL

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hi

i hope to find any one solve my problems with computing course this symster

THE PROBLEM:

7.2 suppose that the following instructions are found at given locations in memory :
20 LDA 50
50 724
51 006
a. show the content of the IR, the PC , the MAR , the MDR ,and A at the conclusion of instruction 20 .

b. Show the contents of each register as each step of the fetch-execute cycle is
performed for instruction 21.

How i can find it?? tell my the way plzzzzz
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### #2 Verst Posted 19 March 2005 - 05:15 AM

Verst

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20 LDA 50
50 724
51 006
I'm writing this by memory so check out the info before you use it...
The IR (Instruction Register) stores the machine code of the current order (code understandable to the processor). Don't know what's the code of the LDA order (load the number at the memory location 50 into register A). You probably have that information somewhere. The PC (Program Counter) is a kind of a pointer that tells the processor where the next instruction is (in the computers memory). It always points at the instruction that comes after the current one. So it probably stores 21.
Can't figure out what MAR and MDR are. Probably registers that stand between the processor and the bus, and are used for temporary storage of data and memory addresses before the processor or the bus can take them.
A is one of the processors registers, at the end of instruction 20 it probably stores the number 724.
Can't answer the b part of the question because it depends on the type of the processor, plus the above should be enough for you to figure out how fetch-execute cycle is performed after reading the literature that came with the course:)
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