Flashcards

DEMA Flash Cards

SEZ McKelvey English 64 cards

Cards in this deck (64)

1Name + Describe the 4 Essential Features of an LMC1. Mailboxes - that have a 2-digit address, so 100 mailboxes is the limit. Each mailbox contains 3 digits
2. Accumulator - can display 3 digits, can add and subtract, has flag for negative results
3. 2 digit program counter with buttons to increment by 1, the other to reset it to 00
4. Input and output trays
2What is the sequence of actions an LM takes in an LMC?Starts by looking at the counter for a mailbox number
Goes to the mailbox and reads what is on the slip of paper there
Takes the appropriate action
Increments the counter
Starts again
3What does LOAD do in an LMC?Go to the mailbox address specified, read the number at that address, then add it to the accumulator
4What does STORE do in an LMC?Go to the calculator, note the number displayed, go to the mailbox address specified and enter that number into it (note the calculator still contains the og number)
5What do ADD and SUBTRACT do in an LMC?Add - go to address specified, read the number at the address, go to the calculator and add that number to the number already on the calc.
Subtract - the same but subtract it
6What do input and output do in an LMC?Input - go to the in tray, read the number, enter that number in the calculator (note this is then removed from the in tray - other inputs may be waiting though and those will remain for future visits. FCFS.)
Output - go to the calculator, read the number there, put hte number in the out tray.
7What does BREAK do in an LMC?The LM has a rest
8What do BRANCH, BRANCH ON ZERO , and BRANCH ON POSITIVE do in an LMC?Branch - set the counter to the 2 digits specified in the address, start fetch again
BRZ - go to the calculator, read the number, if it is zero, set the counter to the 2 digits specified in the address, start fetch again.
BRP - the same as BRZ but do it if the negative flag is not raised.
9what are the main concepts of the von Neumann architecture?- Memory holds both programs and data
- Memory is addressed linearly (ie there is a number for every mailbox)
- Memory is addressed by location (contents are irrelevant)
-Instructions are executed sequentially unless branch/reset occurs.
10What makes the Harvard architecture different to the von Neumman Architecture?- Harvard architecture has separate memory for instructions and data
- Quicker to execute as can access instruction and data at the same time
-It's simpler to follow/analyse code
-Avoids the potential for some malware/bugs due to self-modifying code
11Do modern CPUs use Harvard or von Neumann architecture?They have a CPU cache which partitions instructions and data, giving an "modified Harvard architecture" which is the best of both worlds.
12Name + Describe the 5 major components of a CPUMemory - RAM - "the mailboxes"
Registers - special memory locations that can be accessed very quickly
Arithmetic/Logic Unit - 'the calculator'
Buses - bundles of tiny wires that carry data between components
Control Unit - directs flow of instructions and data within the CPU.
In the diagram, the decoder and multiplexor comprise the control unit.
13What are Registers?They are the "work space" of the CPU. They are storage locations in the CPU, often with a defined purpose and are wired to perform that purpose
They hold binary values temporarily for: storage, manipulation, calculation.
They are manipulated directly by the control unit. Registers can vary in size from 1-128 bits
14What is the accumulator?Accumulator - considered part of the ALU. General purpose registers used for:
holding data
holding interim and final results of arithmetic operations
holding data waiting to be transferred between different memory locations
holding data waiting to be transferred between I/O and main memory
15What are the program counter, instruction register, and flags?PC - holds address of next instruction to be registered
IR - holds the actual instruction being executed
Flags - 1 bit registers used to keep track of special conditions eg arithmetic carry, overflow, power failure etc.
16What are the Memory Address Register and the Memory Data Register?MAR - holds the address of a memory location to be accessed. Is always written to, never from
MDR - holds the value that is being stored to or retrieved from the memory location currently addressed by the MAR. can be written to or from
17What are buses? What are the categories of lines?Buses are the physical connection that makes it possible to transfer data from one location in a system to another. Can transfer data between different points in the CPU, between CPU and main memory, between computer peripherals and CPU
A bus is a group of electrical conductors (lines) used to carry signals. Data, address, control, power are types of lines.
18What are the types of bus? What are bus interface bridges?Point-to-point (bus carries signal from specific source to a specific destination)
Broadcast - bus used to carry signals to many different devices
External bus - ??
Peripheral control interface bus??
USB = universal serial bus
bus interface bridges allow communications between the buses.
19What are the advantages of using hexadecimal?More compact than other number systems, it's easy to convert between binary and hexadecimal.
20How do you translate from binary to hex?Start from radix point, separate binary number into 4 digit nibbles
Translate each group into the hex equvialent, maintaining left to right order.
21How do you translate from binary to hex/Translate each digit into a 4-digit nibble.
22How do you convert from decimal to binary?Divide by two until you reach 0/2, put remainders down right to left from radix point.
23How do you translate decimal fractions to binary?Multiply number by 2 until fractional part is 0. If the ith result of the multiplication is >=1, place 1 in the ith position to the right of the radix,else place a 0 in the ith position to the right of the radix.
24What is the truth table and symbol for an AND gate?
25what is the truth table and symbol for an
26What is the truth table and symbol for a NOT gate?
27What are noise margins and how are they calculated?
28What is the Static Discipline and what are its advantages/disadvantages?The design restriction that you will only allow circuit elements that all satisfy the same logic levels
This means that (given noise limits) you can successfully apply the digital abstraction and combine elements without further concern about logic levels or analogue values
It does reduce your freedom to include arbitrary elements, but makes design much simpler.
29What is the diagram for an nMOS transistor?
30What happens when voltage is applied to an nMOS transistor?The gate is closed and allows current to pass through.
31what is the diagram for a pMOS transistor?
32what happens when voltage is applied to a pMOS transistor?The gate is open and does not allow current to pass through.
33what does an nMOS transistor look like?
34what does a pMOS transistor look like?on at g low and off at g high
35How do you build a not gate with transistors?if A is high then pMOS p1 is off and nMOS n1 is on, so Y is connected to GND - low
if A is low then pMOS p1 is on and nMOS n1 is off, so Y is connected to VDD - high
36how do you make a NAND gate from transistors?
37What is Moore's law?Transistor density doubles every 2 years/computer processing power doubles every 18 months
38What are the 8 simple rules of adding in binary?0+0 = 0
0+1 = 1
1+0=1
1+1=0 with Carry
C +0+0=1
C+0+1=0 with C
C+1+0=0 with C
C+1+1=1 with C
39how many possible Bool operations on k inputs are there? What are the trivial operations, annd what are the other operations?1. 2^2^k
Trivials: 0,1,A,B
Others: Not A, Not B, A, A and B (dot), A or B (+)
Also: adding rule - 0+0 = 0, 0+1 = 1, 1+0=1, 1+1 = 0 with Carry
40What is the truth table and symbol for XOR?
41How do you create XOR from And, Or and Not?A XOR B = (A OR B) AND NOT(A AND B)
42Prove NOR gates are functionally complete (create AND, OR and NOT frmo NOR alone)
43Why are NAND gates often used as universal gates?They use less silicon for the same performance than NOR gates
44What is abstraction? What is discipline? What are the 3 ys of digital design principles?1. Hiding details when they aren't important
2. Restricting design choices when they aren't important
3. Hierarchy - dividing a system into modules and submodules
Modularity - well-defined functions and interfaces for modules
Regularity - encouraging uniformity so modules can be swapped or reused.
45What does a circuit have?one or more discrete valued input terminals. Same for output terminals
A specification of the relationship between inputs and outputs
A specification of the delay between inputs changing and inputs responding
A circuit is made up of elements (each element itself a circuit) and nodes (wires joining elements, whose voltage conveys a discrete valued variable)
46Why do we use combinational logic and what are its rules?Arbitrary circuits can include short circuits and instability, so we restrict what we allow in them. Boolean algebra is used to specify the function of a combinational circuit.
Rules:
1. individual gates are combinational circuits
2. Every circuit element must be a combinational circuit
3. Every node is either an input to the circuit or conneting to exactly one element output
4. The circuit has no cyclic paths - every path through the circuit visits any node at most once.
47Write out sum of products form of this truth table, then simplify.SOP Y=-A-B-C + A-B-C + A-BC + A-B-C
simplified:
Y=-B-C +A-B
48What is the purpose of Karnaugh maps?Graphical way of representing equations to make spotting terms you can simplify easier.
Each cell represents a minterm, and has a zero or 1 depedning on the value of Y corresponding to that minterm. SoP form is given by the 1s
The order of minterms is such that each cell differs in the negation of exactly ONE variable from its neighbours (incl wraparound)
49Draw a Karnaugh map and from that work out SoP from this truth table
50What are the 4 steps to drawing a Karnaugh map?1. create the map so that neighbouring terms differ in the negation of one variable (incl wraparound)
2. circle all rectangular blocks of ones in the map using as few circles as possible
3. Each circle must be 1,2,4 in each dimension
4. Read off the implicants that were circled
If a Boolean expression is minimal then it is the sum of prime implicants: implicants cannot be combined with each other.
51Write simplified SoP from this Karnaugh mapY = A-C + -B
52What are: Combinatorial circuits? Of those, adders, decoders, multiplexors Sequential circuits? of those latches/flip flopsCombinatorial - output depends only on current input.
Adders - add the contents of two registers
Decoders - use a binary number to activate a single line
Multiplexors - use a binary number to select an input
Sequential - output depends on state and input
Latches/flip-flops - basic memory element
53How do you build a full adder (use two half adders)
54How do you add two 4-bit registers by chaining adders?
55How do you build a subtractor?
56What does a decoder do specifically and how do you build one?N inputs, 2^n outputs.
Only one output is high at a time - which one depends on the input
57What is the truth table of a 2-bit decoder?
58Based on the truth table of a 2-bit decoder, how do you build a 2-bit decoder?
59What are the problems with large decoders?Larger decoders require multi input AND gates to construct them in two-level logic, which requires a lot of circuitry for large decoders
Can create deeper circuits with fewer transistors, but you get a slower response.
60What does a Mux do and how do you build a 2-to-1 line mux?Has k+2^k inputs and 1 output
First k inputs (selector) represent a binary number
Output takes the value of the remaining input indexed by this binary number
61What is a tristate? Is it a combinatorial circuit component?Not a combinatorial circuit component, but may be used to build a component that can be part of a combinatorial circuit as it is equivalent to the component built out of logic gates.
Takes two inputs and gives a 0, 1, or floating output
62Why do we use tristates?n channel transistors provide a strong 0 but a weak 1
p channels provide a strong 1 but a weak 0
Rathe than using one to control the output we use both so we get both a strong 1 and a strong 0.
63How do you build a 2-to-1 mux using tristates?
64How do you build a simple ALU using a 32-bit adder, 3 2-1 muxes, a 32-bit AND, a 32-bit OR? Takes A and B, C0 and C1 as inputs one output.