2, Demonstrate a direct mapping procedure to map an opcode into a corresponding

Question

2, Demonstrate a direct mapping procedure to map an opcode into a corresponding microinstruction address considering the following: a. b. c. d. The opcode has 5 bits The mapping should accommodate for routines with upto 8 consecutive microinstructions each The control memory size is 512 words The routines corresponding to various opcodes are to be placed in the second half of the control memory (i.e., starting on memory word 256 and onwards) Q3. Using the microinstruction symbolic language discussed in Chapter 7, convert each of the following microoperations (and the corresponding branching) to a symbolic microinstruction. Show the corresponding binary microinstruction for each. Assume that the microinstructions are stored consecutively at location 0 and that the symbolic address for 64 is DONE. a. b, c. d. AC AC-DR, PC PC +1 (then go to the next microinstruction) DR MARI, AC 0, PC--AR (then jump to the microinstruction at location 64) DR AC (then conditionally branch to address location 64 if AC is zero) AR DR(0-10) (then go to the routine corresponding to the current instruction opcode)

Explanation / Answer

Answer to Q2.

The microinstructions routine are stored at address starting from 256 onwards. Thus starting address of microinstructions is 100000000

Opcode is 5 bits and there are 8 microinstructions per routing.

Thus the opcode XXXXX can be mapped directly as 1XXXXX000 and the range of addresses for the microinstruction routine corresponding to this opcode is 1XXXXX000 to 1XXXXX111

Answer to Q3a)

Symbolic Microinstruction is  

SUB, INCPC        U   JMP   NEXT

Binary Microinstruction in format (Address    F1    F2    F3    CD    BR    AD) is

0000000    000    001   101    00    00    0000001

Answer to Q3b)

Symbolic Microinstruction is  

CLRAC, READ, ARTPC      U   JMP   NEXT

Binary Microinstruction in format (Address    F1    F2    F3    CD    BR    AD) is

0000000    010    100 110    00    00    0000001

Answer to Q3c)

Symbolic Microinstruction is  

ACTDR      Z JMP   DONE

Binary Microinstruction in format (Address    F1    F2    F3    CD    BR    AD) is

0000000    000    101 000    11    00    1000000

Answer to Q3d)

Symbolic Microinstruction is  

DRTAR      U MAP

Binary Microinstruction in format (Address    F1    F2    F3    CD    BR    AD) is

0000000    101    000 000    00    11    0000000

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