Speed comparison between Machine Code and BASIC programs
Assembler coding - Lesson 1
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 $FFD2Here'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 $FFD2More of the same, but this time it would print out ROB on the screen.
Right then, lets see the difference between assembler language and BASIC.
First type and run the BASIC program below:
10 PRINT CHR$(147)
20 PRINT"R"
30 GOTO20You 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 LOOPThis 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)
