jpowcode

Basic assembly code programming is part of the A-level Computing syllabus in the UK. For many programmers the thought of writing in assembly code is extremly tedious. However, the pupils seem to actually quite like it. They like breaking the problems down into their absolute basic components. The excellent Little Man Computer designed by Stuart Madnick models a basic Von Neumann Arctitechture in a web browser. It has an instruction set of only 9 commands so is easy to get started on. I've included some examples of programmes below. They can also be found on my github.

two numbers
Write a program that will prompt for 2 numbers, subtract the first from the second and output the answer, then subtract the second from the first and output the answer.

INP
STA 90
INP
SUB 90
OUT

one to ten up
Write a program to output the numbers 1 to 10 in ascending order.

LDA one
STA count
OUT

loopstart LDA count
          ADD one
          OUT
          STA count
          SUB ten
          BRP loopend
          BRA loopstart
loopend HLT

one     DAT 1
ten     DAT 10
count   DAT

one to ten down
Write a program to output the numbers 1 to 10 in descending order.

LDA ten
STA count
OUT

loopstart LDA count
          SUB one
          BRZ loopend
          OUT
          STA count
          BRA loopstart
loopend HLT

one     DAT 1
ten     DAT 10
count   DAT

count in twos
Write a program to input a number then count up to that number in steps of 2, outputting the sequence.

INP
STA input

loopstart LDA count
          ADD two 
          OUT
          STA count
          SUB input
          BRP loopend 
          BRA loopstart
loopend HLT

one     DAT 1
two     DAT 2
input   DAT
count   DAT

multiply two numbers
Write a program that will input two numbers and multiply them.

INP
STA input1
INP
STA input2

loopstart LDA output
          ADD input2
          STA output
          LDA count
          ADD one
          STA count
          SUB input1
          BRP loopend 
          BRA loopstart

loopend LDA output
        OUT
        HLT

input1  DAT
input2  DAT
count   DAT
output  DAT 0
one     DAT 1

multiply two numbers extended
Extend the program above that it will let the user repeatedly input and multiply pairs of numbers, only stopping if a zero is entered.

start LDA zero
      STA output
      STA count
      INP
      BRZ end
      STA input1
      INP
      BRZ end
      STA input2

loopstart LDA output
          ADD input2
          STA output
          LDA count
          ADD one
          STA count
          SUB input1
          BRP loopend 
         BRA loopstart

loopend LDA output
        OUT
        BRA start

end HLT

input1  DAT
input2  DAT
count   DAT
output  DAT 
one     DAT 1
zero    DAT 0

convert integer to binary
Take as input a positive whole number and output the binary equivalent

start INP
    STA 99

loopstart SUB one
          BRZ loopend
          ADD one
          BRZ loopend
          SUB two
          STA 99
          LDA count
          ADD one
          STA count
          LDA 99
          BRA loopstart

loopend  LDA 99
         OUT
         LDA count
         BRZ end

         STA 99
         LDA reset
         STA count
         LDA 99
         BRA loopstart

end HLT

two     DAT 2
one     DAT 1
count   DAT 0
reset   DAT 0

fibonacci
Take as input the number of terms in the sequence to calculate after 1,1. Output the terms in the sequence 1,1,2,3,5,8,13...

start INP
      STA count
      LDA one
      STA 98
      STA 97
      OUT     
      OUT

loopstart LAD 97
          ADD 98
          STA 99
          OUT
          LDA 98
          STA 97
          LDA 99
          STA 98
          LDA count
          SUB one
          STA count
          BRZ loopend
          BRA loopstart

loopend HLT

one DAT 1
count DAT 0