The following simple algorithm generates a square wave, expressed via the value of R17:

Task: Implement this algorithm in AVR assembly language. Use labels rather than raw jump addresses. The following short example program uses a label (START) rather than specifying the raw jump address:

The following additional AVR instructions may be useful when constructing your algorithm; though you need not use all of them:

The final two instructions (CP and CPI) are perhaps the most interesting-- each of these instructions sets up the ALU to perform a subtraction, but does not write a result back to the register file. These instructions allow you to determine what the flags would be if you were to perform a subtraction, without overwriting the contents of any register.

Square Wave Generator Startup / Reset Initialize R16 and R17 to 0, and R18 to 150.0 Increment R16. Is R16 > R18? No. Yes Logically invert R17. Clear R16. . START: INC RO JMP START; Jump3 to the address represented by the label "START" Mnemonic Operands Description Effect Modifies Z, C, N? COM Ra Rd R18? No. Yes Logically invert R17. Clear R16. . START: INC RO JMP START; Jump3 to the address represented by the label "START" Mnemonic Operands Description Effect Modifies Z, C, N? COM Ra Rd