Answer:

Many answers are possible here. But the shortest one results from observing that if we use those comparators to turn each of these speeds into a boolean 0 or 1, we can take those two lines as a two-bit binary number and supply it as an address to a ROM storing all of the pixel patterns (all x-by-y bits of the pixel board). Then, the output from the ROM could simply be connected directly to the pixel board.

This simple answer is worth full marks. Several students came up with this answer in the exam. Several more produced answers which were close to it. Of course, this was intended to be the "putting it all together" question and I was not surprised that many students left it blank.

There are other possible approaches, but none of them are this simple.

In practice, we probably wouldn't want to design the circuit like this because we would probably have to use a large number of commercial EPROM chips to work this way. A typical EPROM does not have these hundreds of output lines.

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