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Wanna ask some question of our computer structure exam here to be sure. Below is add command of Mic-1 IJVM. We were asked to write new iaddtriple command which will add three top words of stack and store it on the stack again.

iadd1 MAR = SP = SP − 1; rd Read in next-to-top word on stack
iadd2 H = TOS H = top of stack
iadd3 MDR = TOS = MDR + H;wr;go to Main1 Add two top words, write to top of stack

My answer was ;

iaddtriple1 MAR = SP = SP − 1; rd 
iaddtriple2 H = TOS H = 
iaddtriple3 H = MDR = TOS = MDR + H 
iaddtriple4 MAR = SP = SP − 1;
iaddtriple5 MDR = TOS = MDR + H ; wr;go to Main1

I want to ask if my iaddtriple3 step is legal. One of my friends told me that H=blabla +H assignment should be illegal thus shouldn't be used. But time diagram of a data path cycle proves me right. Thanks in advance.

iaddtriple3  H = MDR = TOS = MDR + H
Seki
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Mehmet Çağrı Köse
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1 Answers1

0

It is possible to perform

H = H + MDR

since H can be specified in the C-bus bits, the ALU operation is A + B, the B register is MDR. The actual microinstruction would be 

0003C8000

The first two hex digits could be any numbers, the third hex digit is 0 or 8.

downeyt
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