Control-Lines

Question 1

• Important confusing points:*
• Once we put data in Yin(B) - we can call the command ADD/SUB with another input and Zin to the result is saved in Z.*
• Another info is that the first argument is always placed in Y(the saved register).*
• That is, if we want to substract x-y, then x should be placed in Yin.*

Question 2

• Important points:*
• instead of saving addresses(using brXX) - it is easier to use labels, just recall that we should use lar and not la.*
• not operation changes all bits (1’s complement) - in order to have the last digit use andi R, R , 1*
• Never use address assignment inside a loop. all one-operations should occur once.*

In order to compute imod32 - we should call andi r1, r1, 31

important tip - instead of running from 1000 to 5092, use relative addressing.

• la r1, 4092*
• ld r2, 1000(r1)*
• sub r1,r1,1*
• brpl REPEAT r1*

Question 3

• If each address holds 2 bytes, PC<- PC+2 and M[X] := Mem[X]#Mem[X+1]*
• A and C are helping registers for the ALU unit(with the case of 1 bus)*

Question 4

Memorize!

Answer 4

Question 5

Memorize

Answer 5

Question 6

Glimpse into the condition unit

Note, the can create new condition to help us create new command

Answer 6

Question 7

Great demonstration of how “goto6” works.

It loads 010 into the step counter

Answer 7

Question 8

Name important points regarding the attached image of the control unit

Answer 8

• All control signals have an expression at the output of the control unit
• A control signal is implemented using relations between:
  
  • Opcode which is using it
  • Conditions: other signals from the data path - CON, n=0
  • Interrupts and other external signals
  • Control step decoder

Question 9

Note the way goto7 is implemented such that if it gets 1 it load the step counter

Question 10

Important points regarding control signal language:

• CONin -> the system knows we want to use a condition. We just need to specifiy who is to be checked.
• All ALU operations go to C. Anyway - excepts for C=B, we should mention Cin
• ld operation always put the output in n, and by output we mean 5 LSB’s on bus.
  
  • if n = 5 it means the “goto” operation occurs 6 times because n=0 is still a valid state.
• Conditional control signals: CON,n=0, are written the same in RTN and as a control signal.

Question 11

Amazing solution for this problem

Note that the “end” control signal tells the program to end.

If it appears in a general case: the program ends..

If it appears for COND-> it ends the program only if COND=1.

Answer 11