Questions for Section 1: Solutions Guide
1. Boolean data set is {True, False};
Byte data set is {-128, -127, …, 0, 1, …127}
Short data set is {-32, 768, …, 0, 1, … 32767}1
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Character data set is the set of all characters representable in 16-bit Unicode (older languages used ASCII)
2. See Chapter 2
3. Because in digital transmission the receiver has only a finite number of allowable values (in binary that is just two values: low and high). If noise changes the signal from one of these values by a small amount it will be at a non-allowable value (e.g. between low and high). When the receiver sees this, it will round off to the nearest allowable value. The assumption is that noise of low height is always more likely than large so most of the time the nearest value will be the one sent the one sent.
In analogue transmission, every value the signal can take, represents something different so no matter what the receiver gets, it looks like an OK value and there is no way of telling if it was the one sent or was changed while travelling. Thus the receiver has no way of eliminating any noise that adds to the signal.
4. Because the answer may lie outside the range of the code. E.g if an 8-bit unsigned number code can represent numbers from 0 to 255 and we input the 8-bit codewords for 255 and 1 to the adder, it would need to give out the 8-bit codeword for 256. But there is no such codeword in the code. The adder will output 0 instead, which is the wrong answer. We call this an overflow. See Section 2 for a discussion of this.
5. The bit time is the shortest time that a driver can keep the wire it is driving at one of the allowed values (e.g. low or high) to be sure the receiver can measure it correctly. This applies individually to every wire in a bus (which is just a set of parallel wires running alongside each other) since each such wire will have its own driver (e.g. making it go low or high) and its own receiver.
6. A register will need a line to tell it when to enter new data (e.g. 0 means keep existing; 1 means write new). May also need a line to say: ¡°I want to read your content¡± if the register is designed so that it does not reveal its content all the time: for example some registers are designed to keep all outputs low unless told to show what is stored.
1 Question. Why have numeric codes of different sizes (Java also has a 32-bit one and a 64-bit one)? Two reasons: (1) A short code takes up less space if it¡¯s all you need and that can matter if you have a lot of data to store; (2) If you know you will always be working with small values, having a code with low limits may help catch programming errors.
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