LIttle Man Computing (Using&Memory)

 

                                       Little Man Computer (Load Save)

Program

INP
STA FIRST
INP
STA SECOND
LDA FIRST
OUT
LDA SECOND
OUT
HLT
FIRST DAT
SECOND DAT

What you should do

1. Click on the "LMC Simulator Applet" link to start the LMC simulator.
2. Clear the Message Box and all of the LMC mailboxes -- click the "Clear Messages" button and the "Clear" button if necessary.
3. Copy the eleven line program above and paste it into the Message Box
4. Click on the "Compile Program" button.
5. Click on the "Run" button.
6. When prompted, enter three-digit numbers in the "In-Box", and press the "Enter" button.

What you should see

• After the program is compiled, you should see from mailbox 0 to 7 the instructions 901, 309, 901, 310, 509, 902, 510, 902.  The Program Counter should start at 0 (click on "Reset" if necessary).
• DAT is the tenth and eleventh instruction of your program, so they refer to mailboxes 9 and 10 (0-indexed counting).  FIRST and SECOND are the identifiers that have been declared to represent these mailboxes in the assembly language program.
• When you click on "Run" or "Step", the Message Box will describe the actions of each instruction.
• After the first INP instruction, the Accumulator has a copy of the first value entered in the In Box.
• After the STA instruction, the input value is copied from the Accumulator to mailbox 9 -- 3 means STORE and 09 refers to the mailbox to store into.
• After the second INP instruction, the Accumulator has a copy of the second value entered into the In Box (use a different value than the first).
• After the second STA instruction, the second input value is copied from the Accumulator to mailbox 10.
• After the LDA instruction, the Accumulator is reset to the first input value.  This value has been retrieved from mailbox 9 -- 5 means LOAD and 09 refers to the mailbox to load from.  Note: since your Accumulator can only work on one value at a time, you have to repeatedly STORE and LOAD values from memory to keep them from getting erased by the next operation.
• After the OUT instruction, the Out Box has a copy of the value in the Accumulator -- the first input value.