Speed comparison between Machine Code and BASIC programs

Assembler coding - Lesson 1

eZine lover (@eZine)

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Assembler coding

 · 24 Nov 2022

Printing a character on the screen

This first example shows you how to print a character on the screen. In the example you make use of the 'accumulator' acc. for short, and a 'Kernal Routine'. Here's the program

  10 ORG 8192 
  20 LDA #82 
  30 JSR $FFD2

Here's the breakdown

• 10 - Assemble in location 8192 decimal (2000 hex) - Type SYS 8192 to run from BASIC
• 20 - Puts the value 82 decimal into the accumulator (value for the letter R)
• 30 - This jumps to a kernal subroutine that prints the value in the acc. to the screen

Ok, so know you could write your name like this

  10 ORG 8192 
  20 LDA #82 
  30 JSR $FFD2 
  40 LDA #79 
  50 JSR $FFD2 
  60 LDA #66 
  70 JSR $FFD2

More of the same, but this time it would print out ROB on the screen.

Right then, lets see the difference between assembler language and BASIC.

First type and run the BASIC program below:

  10 PRINT CHR$(147) 
  20 PRINT"R" 
  30 GOTO20

You should see your screen fill with the letter R. Notice the speed at which this happens.

Now lets assemble the machine code equivalent and see the execution speed difference.

Type in the following in Zeus, assemble it and run it.

  10 ORG 8192 
  20 LDA #147 
  30 JSR $FFD2 
  40 LDA #82 
  50 LOOP JSR $FFD2 
  60 JMP LOOP

This is the assembler version of the basic program. When you have assembled it, use: SYS 8192 from BASIC to run it. Again the screen will fill with the letter R, only this time much faster.

The assembler version works like this:

• 10 - Place in memory to put the code (Execute using SYS 8192 from BASIC)
• 20 - Place value for clear screen in accumulator
• 30 - Print character by jumping to Kernal Subroutine
• 40 - Place value for letter 'R' in accumulator
• 50 - Print character by jumping to Kernal Subroutine
• 60 - Jump to the label named loop (i.e. Line 50)