Control bits for input of A register

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Control bits for input of A register

learning67
I was initially applying the logic that the And of the i-bit and d1 bit is used as the select line for Mux that gives the input to the A register.
But this fails when I want to perform A=A+1 because the i bit=1 d1 bit=1 and it loads the instruction when it should load the value after execution into the A register.
How do I approach this problem? Any help provided will be great!
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Re: Control bits for input of A register

cadet1620
Administrator
learning67 wrote
I was initially applying the logic that the And of the i-bit and d1 bit is used as the select line for Mux that gives the input to the A register.
But this fails when I want to perform A=A+1 because the i bit=1 d1 bit=1 and it loads the instruction when it should load the value after execution into the A register.
How do I approach this problem? Any help provided will be great!
This Mux selects the data source for the two types of instructions that load values into the A register.

A-instructions load the instruction itself into the A register, and C-instructions with d1=1 load the ALU output into A.

Think about this:

Does it matter what the Mux selects during C-instructions with d1=0?
When must the input to the A register not be the ALU output?

--Mark
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Re: Control bits for input of A register

learning67
Thank you the hints helped a lot!

Built the computer :D
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