Question

It’s been a while since my assembly class in college (20 years to be exact).

When someone gives you a number, say 19444, and says that X is bits 15 through 8 and Y are bits 7 through 0… how do I calculate values of X and Y?

I promise this is not homework, just a software guy unwisely trying to do some firmware programming.

Answer 1

First of all convert the input number to hexadecimal:

19444 => 0x4BF4

Hex is convenient because every 4 binary bits are one hex digit. Hence, every 2 hex digits are 8 bits, or a byte. Now assuming traditional little-endian notation (look it up!), bits 7 downto 0 are the low byte, bits 15 downto 8 are the high byte:

   [7:0] => 0xF4
   [15:8] => 0x4B