LMC practice

The table below shows the Little Man Computer instruction set.

Mnemonic	Instruction
`ADD`	Add
`SUB`	Subtract
`STA`	Store Accumulator
`LDA`	Load Accumulator
`BRA`	Branch Always
`BRZ`	Branch when Zero
`BRP`	Branch when Positive or zero
`INP`	Input
`OUT`	Output
`HLT`\|`COB`	End program

Complete the table above to show the missing mnemonics and instructions.

Write a program using the Little Man Computer instruction set that will allow a user to input two numbers and then output the larger of the two numbers. The program should loop continuously.

        INP
        STA     a
        INP
        STA     b
        SUB     a
        BRP     out_b
        LDA     a
        OUT
        BRA     0
out_b   LDA     b
        OUT
        BRA     0
a       DAT
b       DAT

Also:

        DAT     901
        DAT     312
        DAT     901
        DAT     313
        DAT     212
        DAT     809
        DAT     512
        DAT     902
        DAT     600
        DAT     513
        DAT     902
        DAT     600

Try it online: https://starwort.github.io/lmc/

Below is part of a program written using the Little Man Computer instruction set. This section of code can exit by either jumping to the code labelled pass or fail depending on what value is in the accumulator when the code is run.
```
test    SUB     ten
        BRZ     pass
        BRP     test
        BRA     fail
ten     DAT     10
```
1. Explain what the following line does:
```
ten     DAT     10
```
  - The line declares a named mailbox 'ten' which is initialised to the literal value 10.
2. Complete the table below determining whether the program branches to pass or fail given the following values in the Accumulator when it is run.
  
  Starting value in Accumulator Jump Target
  
  29 fail
  
  30 pass
  
  31 fail
3. The complete program is shown below:
```
        INP
main    STA     entry
        BRA     test
fail    LDA     entry
        ADD     one
        BRA     main

test    SUB     ten
        BRZ     pass
        BRP     test
        BRA     fail

pass    LDA     entry
        OUT
        HLT

entry   DAT
ten     DAT     10
one     DAT     1
```
  1. Give one instruction in the program that, when executed, changes the value in the Accumulator.
    - INP
  2. Give one instruction in the program that, when executed, changes the value in the Program Counter.
    - BRA test
  3. State the value the code outputs for the input 18.
    - 20
  4. State the value the code outputs for the input 37.
    - 40
  5. Describe the purpose of the program.
    - Round the input to the next multiple of 10.

Starting value in Accumulator	Jump Target
29	`fail`
30	`pass`
31	`fail`