The Little Man Computer¶

Background¶

Example¶

What does the following LMC program do?

901 310 901 311 110 902 510 211 902 000

Example¶

What about this one?

604 060 040 001 501 108 308 502 300 902 203 717 302 508 103 308 607 000

Example¶

Maximum of two numbers.

"Assembler" code¶

        INP
        STA x
        INP
        STA y
        SUB x
        BRP second
        LDA x
        BRA done
second  LDA y
done    OUT
        HLT
x       DAT
y       DAT

Translating to machine code¶

00  901            INP
01  311            STA x
02  901            INP
03  312            STA y
04  211            SUB x
05  808            BRP second
06  511            LDA x
07  609            BRA done
08  512    second  LDA y
09  902    done    OUT
10  000            HLT
11         x       DAT
12         y       DAT

901 311 901 312 211 808 511 609 512 902 000

Example¶

LMC Simulator

        INP
        STA x
        INP
        STA y
loop    BRZ done
        LDA ans
        ADD x
        STA ans
        LDA y
        SUB one
        STA y
        BRA loop
done    LDA ans
        OUT
        HLT
one     DAT 1
ans     DAT 0
x       DAT
y       DAT

Exercise¶

Modify the program above to compute the minimum of the two numbers. Create a new "Markdown" cell below this cell, and enter your program there. Include both the assembler code and machine code for your program. (The idea is for you to practice working with the jupyter notebook interface as well as thinking about the algorithm.) The Little Man instruction set can be found here and the Little Man simulator here.

(HINT: To edit a Markdown cell, double click it. To stop editing and typeset the cell, press SHIFT+ENTER. You can learn more about the Markdown format under the "Help" menu above. See the above cell for formatting ideas for the program.)

00 INP
01 STA 11
02 INP
03 STA 12
04 SUB 11
05 BRP 08
06 BRZ 08
07 LDA 11
08 BRA 09
09 LDA 12
10 OUT
11 HLT
12 DAT 00
13 DAT 00

901 311 901 312 211 808 708 511 609 512 902 000