In this challenge we will create a computer program using LMC (Little Man Computer) that takes two inputs and outputs the larger (max) of the the two inputs.
By completing this challenge we will investigate the use of the branching instructions BRP and BRA to create an IF THEN ELSE selection.
We have produced the flowchart of our max algorithm using LMC instructions:
You can now type and test this code using one of the following online LMC Simulators:
LMC Instruction Set
Note that in the following table “xx” refers to a memory address (aka mailbox) in the RAM. The online LMC simulator has 100 different mailboxes in the RAM ranging from 00 to 99.
|INP||INPUT||Retrieve user input and stores it in the accumulator.||901|
|OUT||OUTPUT||Output the value stored in the accumulator.||902|
|LDA||LOAD||Load the Accumulator with the contents of the memory address given.||5xx|
|STA||STORE||Store the value in the Accumulator in the memory address given.||3xx|
|ADD||ADD||Add the contents of the memory address to the Accumulator||1xx|
|SUB||SUBTRACT||Subtract the contents of the memory address from the Accumulator||2xx|
|BRP||BRANCH IF POSITIVE||Branch/Jump to the address given if the Accumulator is zero or positive.||8xx|
|BRZ||BRANCH IF ZERO||Branch/Jump to the address given if the Accumulator is zero.||7xx|
|BRA||BRANCH ALWAYS||Branch/Jump to the address given.||6xx|
|HLT||HALT||Stop the code||000|
|DAT||DATA LOCATION||Used to associate a label to a free memory address. An optional value can also be used to be stored at the memory address.|