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Flashcards in Part 1 Deck (40)
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1

Why does it matter how many bits you use for a given data type?

arithmetic operations on larger bits of data (i.e. 32 bit) generate more heat than say 8 bit data

2

How many numbers can be stored in an unsigned 8 bit representation AND from which number until which one.

256. From 0 to 255

3

What is wrong with sign-magnitude representation?

It wastes one number in 0 and -0 and allows only a range from -127 unitl 127. Only 255 numbers

4

How does 2s complement representation work?

It's an alternative to sign-magnitude and it works by changing the value of the MBS from positive to negative

5

What are the benefits of 2s complement?

It allows a range of 256 numbers and the circuitry for addition is the same as for subtraction- -128 to 127

6

What is a disadvantage of 2s complement

When you are subtracting a smaller number from a larger number you get a lot of negative numbers which translates into a lot of bit flips generating a lot of heat

7

What's wrong with floating point numbers?

Precision: Dividing a very large number by a very small one might result in an inaccurate output

8

What is the definition of a proposition?

We can tell whether statement is true or false and it's unambiguous. "It is true that"

9

What is the complement of: e = x or y or z

(not)e = (not)x and (not)y and (not)z

10

Minterms and maxterms. Where do they appear? and what are they equivalent to?

Minterms are products and appear in DNF. Maxterms are sums and appear in CNF

11

What is the difference between a PMOS and a NMOS transistor?

PMOS is initially closed and allows current to flow. It opens when applied 1. NMOS is initially open and closes when applied a 1

12

In an inverter, which transistor is open and which is closed when A is set to VDD

NMOS (0) transistor is closed setting Q to VSS and PMOS is open (1)

13

What logic gates are used for the sum and carry outputs in an adder respectively?

sum: xor
carry: and

14

When is XOR defined to be true for multiple arguments?

If and only if an odd number of args is true (a XOR b XOR c)

15

What is the (negative) implication of implementing a ripple-carry adder?

You have to wait for the signal to propagate to know the value of higher order bits

16

Why do we need log2(N) number of select bits when N = number of signals to select from?

Because N represents the number of select signals we have and we need the appropriate number of bits to represent that amount of singals. I.e to represent 8 (select signals) we need 3 bits (which can represent up to 8 combinations)

17

What is the difference between a multiplexor and a demultiplexor?

A multiplexor selects which input signal to propagate whereas a demultiplexor selects into which output signal to propagate the (single) input signal

18

What is a ring oscillator?

Device composed of an odd number of inverters chained together. The output of the chain is made as an input to the start of the chain and the output oscillates between 2 voltage levels

19

What does setting and resetting the latch mean in an SR latch?

Setting means activating S and resetting means activating R. Since the input singals are active low this means that S is activated when made 0 and R the same

20

Which is the "not allowed" output in an SR latch and why is it not allowed?

When both inputs equal 0. It is not allowed because in this scenario both outputs would be equal to each other (1) which defeats the point of an SR latch. Q and Q' are supposed to be inverted.

21

How does a D latch work and what is its benefit over the SR latch?

It has 2 inputs. 1 single data input and a enable/disable (propagation) input which when set to 0 disables propagation and stores data value. The benefit it has is that it eliminates the"DE" part of the latch eliminates possibility of a "0 0" input on the SR part of the latch (which is an SR latch itself) which is the "not allowed" value

22

What is "level sensitive" and "edge sensitive" and what are examples of devices that implement these concepts?

Level sensitiveness happens when a singal can be propagated when the clock singal is "on" or 1. An example of this are latches (i.e. D latch). Edge sensitiveness happens when a singal is propagated when the clock signal rises from 0 to 1 (but not WHILE it is 1). An example of this are flip flops (i.e. JK flip flops)

23

What are timing cosntraints used for?

When a data singal changes, there's a small period of time when we don't know what is its value so timing cosntraints are used to avoid unexpected behaviour. A setup time and hold time are set to define how long before the event (clock edge) and after the event the singal should be settled

24

Why does the second latch in a master slave flip flop need to have the enabler inverted?

The inverter prevents the data value from being propagated unless initial enabler value is 0 (which would be 1 in second D latch) enabling the data value to reach the second input and simulate only changing when falling. Basically prevents racing and replaces it with toggling

25

What are the benefits of a JK flip flop?

If you compare it with an SR flip flop, it gets rid of the "not allowed" SR values 0 0.

26

What is the problem of a simple JK flip flop and why do we need a master slave configuration?

The problem is that input values "1 1" lead to racing behaviour which can be eliminated by controlling it via the master slave configuration. This leads to toggling behaviour instead of an uncontrolled switching between 0 and 1 for the outputs.

27

Why need for inverter for the clk value in master slave config of JK flip flop?

Because it makes only master OR slave operational at any given clock tick

28

From a high level perspective, how do you read and write from a memory address?

Writing: specify that we are writing (1), set address to location, set data wires to value we want to store, hold this for the required amount of time(clock edge) so content of address changes to value of data
Reading: specify we are reading(0), set address to location, hold for required amount of time and data from location appears in data wires

29

What does random access mean in RAM?

Each memory cell can be written or read in any order regardless of the previous cell that was accessed

30

From a lower level perspective, how does reading and writing work in an SRAM cell?

Reading: Wordline set to 1 to allow value within the bi-stable circuit to propagate to the bitline
Writing: Set BL to nQ and BL’ to nQ’, set worldline to 1 and allow to propagate to Q and Q’ respectively