Bit-reverse a byte on 68HC12

assembly bit-manipulation reverse codewarrior 68hc12
dohlfhauldhagen picture dohlfhauldhagen · Feb 7, 2011 · Viewed 25.4k times · Source

I'm in a microprocessors class and we are using assembly language in Freescale CodeWarrior to program a 68HCS12 micro controller. Our assignment this week is to revers a byte, so if the byte was 00000001, the output would be 10000000, or 00101011 to 11010100. We have to use assembly language, and were told we could use rotates and shifts (but not limited to!) to accomplish this task. I'm really at a loss as to where I should start.

Answer

Spacedman picture Spacedman · Feb 7, 2011

Hints: If you do a shift, one bit gets shifted out and a zero (probably) gets shifted in. Where does that shifted out bit go to? You need to shift that in to the other end of the destination register or memory address.

I'm sure that 25 years ago I could do this in Z80 machine code without an assembler :)

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