lesson 1

PROGRAMMING IN ASSEMBLY
BY STEVE BJORK
LESSON 1 –FOUNDATION – IT’S ALL ABOUT THE MATH

HOW MATH WORKS ON THE 6809 CPU
•Digital Electronics has only two states.
•Zero or off
•One or on
•The more states a digit has the more likely to create an error
•With digital, it’s hard to make an error.
•Digital or Binary is also easier for the CPU to do the math.

HOW MATH WORKS ON THE 6809 CPU
•How to do larger numbers
•Our normal math, Decimal or Base-Ten has 10 states per digit.
•0-1-2-3-4-5-6-7-8-9
•Binary or Base-Two has only two states per digit.
•0-1
•In Base-Ten math, we can add more Digits to work with numbers
greater than 9.
•The same is true with Base-Two math.

HOW MATH WORKS ON THE 6809 CPU
1,000 100 10 1
0 2 4 5
0*(1000) + 2*(100) + 4*(10) + 5*(1) = 245
Using extra digits for larger number like 245 in Base Ten.
Using extra digits for larger numbers like 245 in Base Two.
128 64 32 16 8 4 2 1
11110101
1*(128) + 1*(64) + 1*(32) + 1*(16) + 0*(8) + 1*(4) + 0*(2) + 1*(1) = 245

HOW MATH WORKS ON THE 6809 CPU
•With so many digits in binary, sometimes we use Base-Sixteen.
•Hexadecimal –Think 6 + 10 or 16 digits.
•The numbers are 0-1-2-3-4-5-6-7-8-9-A-B-C-D-E-F.
•A=10, B=11, C=12, D=13, E=14 and F=15.
•Using extra digits for larger numbers like 245 in Base-Sixteen.
256 16 1
15 5
0*(256) + 15*(16) + 5*(1) = 245 or ($F5 in Hexadecimal)