Little Man Computer – Burglar Alarm

Posted on April 28, 2017 by Administrator Posted in Computer Science, Computing Concepts, Little Man Computer (LMC), Solved Challenges

Write an LMC program to let the user enter a PIN code to deactivate a burglar alarm.

The program should let the user have up to 3 attempts to enter the correct PIN code before starting the alarm.

The correct PIN code is “123”.

If the user gets the right PIN code the program should output value 1.
If the user gets the wrong PIN code the program should output value 9 indicating that they can have another go at entering the PIN code.
If after three attempts the PIN code entered is still incorrect, the program should output value -1.

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.

Mnemonic	Name	Description	Op Code
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.