Quick Answer
Cornmeal does not use the same grams-to-cups value as every other ingredient. Using a practical US cup reference, 138 grams of cornmeal is about 1 cup.
That means 100 grams of cornmeal is about 0.72 cups, while 200 grams is about 1.45 cups.
Cornmeal is a medium-density dry ingredient. One US cup of cornmeal weighs around 138 grams depending on coarseness and packing.