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The operation to manipulate the direction bit is 1 to 6400 times 2. The first 6400 has the direction bit set LOW then the next 6400 the direction bit is set HIGH. The variable onerev is set at a constant value of 6400. The variable oneway is incremented each loop. If its value is less than 6400 then the direction bit is set LOW and if its value is higher than 6400 then the direction bit is set HIGH. Remember this code loops endlessly, so the value of oneway changes each loop. I suppose the variable oneway should be changed to a constant.