Midterm 2 -- Closed book section

27 April, 1995

The entire exam is to be turned in at 5:45 PM. Work the closed book section first and turn it in before you consult your books and notes to work on the open book section.

Problem 1 (7 points)

In Figure 10-5 (p. 341), the Q register is used for both the multiplier and the product. Explain how one register can be used for two very different purposes. In particular, point out what is contained in the Q register at the end of the i'th step of the multiplication.

Problem 2 (7 points)

What is the largest possible positive number that can be represented in a 32-bit float point number that uses 23-bit mantissas and 8-bit exponents encoded using excess-127 notation? Writing the bit pattern is an acceptable answer.

Problem 3 (7 points)

Why are the read and write control lines in a DMA controller bidirectional? Under what condition and for what purpose are they used as inputs? Under what condition and for what purpose are they used as outputs?

[This is question 11-27 from page 441 of the textbook.]

Problem 4 (7 points)

Why does DMA have priority over the CPU when both request a memory transfer?

[This is question 11-30 from page 442 of the textbook.]

Problem 5 (7 points)

Most likely, the CPU communicates with its interface units with strobe transfers while the interface units communicate with their I/O devices with handshaking. Why are different methods are used for these two similar tasks.

Problem 6 (7 points)

What would it mean to say that an asynchronous serial transmission protocol has 1.5 stop bits? How can you have half a bit?

Problem 7 (4 points)

List two "slow" peripherals found on a typical PC?

Problem 8 (4 points)

List two fast peripherals found on a typical PC?

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