Assembler Document!

The Project is a very Simple Assembler that translate the assembly code to machine code for the Basic Computer Instruction Set Architecture as per M.Mano's book "Computer System Architecture"

The Basic Computer has a 16-bit instruction divided into 12-bit address, 3-bit opcode and 1-bit for addressing mode.

Instructions set:

- Memory Reference Instructions:

        direct - indirect [Addressing]
    and 000    - 1000
    add 001    - 1001
    lda 010    - 1010
    sta 011    - 1011
    bun 100    - 1100
    bsa 101    - 1101
    isz 110    - 1110

- Register reference Instructions

    cla 0111100000000000
    cle 0111010000000000
    cma 0111001000000000
    cme 0111000100000000
    cir 0111000010000000 
    cil 0111000001000000
    inc 0111000000100000
    spa 0111000000010000
    sna 0111000000001000
    sza 0111000000000100 
    sze 0111000000000010
    hlt 0111000000000001

- Input Output Instructions

    inp 1111100000000000
    out 1111010000000000
    ski 1111001000000000
    sko 1111000100000000
    ion 1111000010000000 
    iof 1111000001000000

There are only 4 pseudo-instructions supported by this assembler: ORG, END, HEX and DEC. These instructions do not have a direct binary mapping, but are instructions to the assembler to behave in a certain way during the first and second passes.

First Test Case

    ORG     100     / Origin of program is location 0x100
    LDA     SUB     / Load subtrahend to AC
    CMA             / Complement AC
    INC             / Increment AC
    ADD     MIN     / Add minuend to AC
    STA     DIF     / Store difference
    HLT             / Halt computer

MIN, DEC 83 / Minuend SUB, DEC -23 / Subtrahend DIF, HEX 0 / Difference stored here END / End of symbolic program

Output of first test case

    -------------------- Symbol Table -----------------------
    MIN  :  106
    SUB  :  107
    DIF  :  108
    ---------------------------------------------------------
    -------------------- Machine Code -----------------------
    100  :  0010000100000111
    101  :  0111001000000000
    102  :  0111000000100000
    103  :  0001000100000110
    104  :  0011000100001000
    105  :  0111000000000001
    106  :  0000000001010011
    107  :  1111111111101001
    108  :  0000000000000000
    ---------------------------------------------------------

Second Test Case

    ORG 0      /Origin of program is location 0
    LDA A     /Load operand from location A
    ADD B     /Add operand from location B
    STA C     /Store sum in location C
    HLT       /Halt computer

A, DEC 83 /Decimal operand B, DEC -23 /Decimal operand C, DEC 0 /Sum stored in location C

    END      /End of symbolic program       

Output of second test case

    -------------------- Symbol Table -----------------------
    C  :  6
    A  :  4
    B  :  5
    ---------------------------------------------------------
    -------------------- Machine Code -----------------------
    0  :  0010000000000100
    1  :  0001000000000101
    2  :  0011000000000110
    3  :  0111000000000001
    4  :  0000000001010011
    5  :  1111111111101001
    6  :  0000000000000000
    ---------------------------------------------------------

Third Test Case

    ORG 0      /Origin of program is location 0
    LDA A  I   /Load operand from location A
    ADD B     /Add operand from location B
    STA C     /Store sum in location C
    HLT       /Halt computer

A, DEC 83 /Decimal operand B, DEC -23 /Decimal operand C, DEC 0 /Sum stored in location C

    END      /End of symbolic program       

Output of third test case

    -------------------- Symbol Table -----------------------
    A  :  4
    B  :  5
    C  :  6
    ---------------------------------------------------------
    -------------------- Machine Code -----------------------
    0  :  1010000001010011
    1  :  0001000000000101
    2  :  0011000000000110
    3  :  0111000000000001
    4  :  0000000001010011
    5  :  1111111111101001
    6  :  0000000000000000
    ---------------------------------------------------------

Fourth Test Case

            ORG     aaa     / Origin of program is location 0x100
            LDA     SUB     / Load subtrahend to AC
            CMA             / Complement AC
            INC             / Increment AC
            ADD     MIN      / Add minuend to AC
            STA     DIF     / Store difference
            HLT             / Halt computer

    MIN,    DEC     83      / Minuend
    SUB,    DEC     -23     / Subtrahend
    DIF,    HEX     0       / Difference stored here
            END             / End of symbolic program

Output of Fourth Test Case

    -------------------- Symbol Table -----------------------
    MIN  :  ab0
    SUB  :  ab1
    DIF  :  ab2
    ---------------------------------------------------------
    -------------------- Machine Code -----------------------
    aaa  :  0010101010110001
    aab  :  0111001000000000
    aac  :  0111000000100000
    aad  :  0001101010110000
    aae  :  0011101010110010
    aaf  :  0111000000000001
    ab0  :  0000000001010011
    ab1  :  1111111111101001
    ab2  :  0000000000000000
    ---------------------------------------------------------