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Module 5 > 5.4 Data Buses > Flashcards

5.4 Data Buses Flashcards

1
Q

Why is electricity the ideal means to transmit information?

A

Because it travels at the speed of light.

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2
Q

Ideally no current flows on a digital data line, There is only a real small amount sufficient to do what?

A

Forward or reverse bias semiconductor P and N Junctions

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3
Q

Data bus line have a signal transmitted across them no higher than?

A

5 Volts DC

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4
Q

What component is providing the 1’s and 0’s?

A

Transistors switching on and off.

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5
Q

With the transistors continually going from forward to reverse bias what does the sine wave look like?

A

A distorted sine wave.

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6
Q

What represents Binary 0 of a data signal?

A

0 volts (0 - 0.8V Not sufficient to saturate a transistor)

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7
Q

What represents Binary 1 of a data signal?

A

Between 2 and 5 Volts.

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8
Q

The transmitter and receiver are synchronized by the same clock pulse, when the transmitter is outputting a high what does the receiver do?

A

Detects it and clocks it through as a 1 to processing circuitry.

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9
Q

When using analogue to send signals what must be considered?

A

Voltage must be EXACT, any deviation will cause errors. this is why Digital is mainly used.

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10
Q

What are the 2 basic ways to move data between parts of a system?

A

Parallel data transfer and serial data transfer.

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11
Q

With serial transfer, each bit of data is transferred from?

A

A Store (Memory location)

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12
Q

Describe the operation of a Serial Data Transfer

A

Data triggered by clock pulse, transmitter and receiver are now synced, data arrives at receiver from transmitter and sequentially stored in MEMORY before transferred to processing circuitry.

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13
Q

How is the data transmitted on a serial bus?

A

Sequentially, one word following another word.

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14
Q

Advantages of Serial Data Bus

A
  1. Long Distance
  2. Less H/ware
  3. Less weight and space.
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15
Q

How can you speed up the data transfer of a Serial data bus?

A

Multiplexing.

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16
Q

With parallel transfer, each bit is taken from?

A

A separate circuit and is transmitted over a separate line.

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17
Q

Serial data transfer is typical of?

A

Data bus communications

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18
Q

Advantages of parallel data transfer?

A

Much faster

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19
Q

What are the disadvantages of parallel data transfer?

A

Lots more hardware, increases space and weight.

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20
Q

Once a signal is inside a computer it is typically processed in?

A

Parallel

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21
Q

An 8 and 64 bit parallel bus would be how many times faster than a serial bus?

A

8 times and 64 times faster.

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22
Q

A parallel bus typically interconnects the internal devices of a computer and has enough wires to?

A

Transmit all bits of the word simultaneously.

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23
Q

What technique is used to carry many different signals by one conductor with multiplexing?

A

Digital ‘time division’ Technique

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24
Q

Define multiplexing

A

Combing 2 or more information channels onto a common transmission medium.

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25
Q

Multiplexing is usually done by?

A

Logic gates responding in sequence to clock pulse signals.

26
Q

How are analogue signals multiplexed?

A

First converted to digital transmitted across the multiplex network then transmitted back to analogue.

27
Q

Describe the operation of a multiplexing system,

A
  1. At the multiplexing end signal on each input line is sampled and passed onto the common transmission when the AND gates are clocked ON!
    2.The sequenced gate outputs are serially transmitted to the demultiplexer.
  2. As each AND gate is clocked ON, it passes the signal that is ON THE transmission line AT THAT TIME.
  3. Having the effect of transmitting 8 separate inputs through 8 separate outputs over the SAME transmission line.
28
Q

What is a additional side benefit of digital data over analogue?

A

Digital data can be transferred bi-directionally, analogue is unidirectional.

29
Q

The interface between each computer and external device is accomplished via?

A

The digital data bus, made up of a twisted pair of wires which are shielded and jacketed.

30
Q

Why is the digital data bus shielded and jacketed?

A

Provide spike protection and eliminate EMF induced errors.

31
Q

Why is the digital data bus a pair of twisted wires?

A

So the magnetic fields induced by the currents flowing through them will cancel each other out.

32
Q

Transmission of data between transmissions and components is accomplished with?

A

8,16,32 or 64-bit digital words.

33
Q

All communication is controlled by either bus controllers or by timing regimes. they transmit only?

A

One data word on the data bus at any one time.

34
Q

The multiplexer bus functions like a highway, connected to manage all data transmitted over the highway. what is used to connect peripheral components to the highway?

A

Breakouts (Couplers)

35
Q

How many bus controllers can be active at any one time?

A

One!

36
Q

What parameters does the bus controller control?

A

Transfer of data, control and management of the bus.(mode commands)

37
Q

Data transmission is strictly controlled by?

A

The bus controller.

38
Q

How does the bus controller operate?

A

By sending out commands to peripheral systems REQUESTING data which is stored in the memory of the peripheral components.

39
Q

MIL-STD-1553 defines?

A

Electrical and protocol characteristics for a data bus.

40
Q

MIL-STD-1553B defines the term time division multiplexing as?

A

Transmission of information from several signal sources through one communications system with different signal samples staggered in time to form a COMPOSITE PULSE TRAIN.

41
Q

Easy way to describe MIL-STD-1553B

A

Data can be transferred between multiple avionics units over a single transmission media, taking place at different moments in time.

42
Q

What are the 3 distinct word types that MIL-STD-1553 uses?

A

Command words, data words, status words.

43
Q

All 3 word types (Command, Data, Status) have a common structure what is this?(MIL-STD-1553)

A

1.Each word 20 bits in length
2. First 3 bits are used as synchro field. allowing all device clocks to resync at beginning of each word.
3. Next 16 bits are the information field (different between the 3 types)
4. The last bit is the parity bit.

44
Q

Describe Parity?(MIL-STD-1553)

A

Based on odd parity for the single word, encoder automatically calculates parity, odd parity, there is always an ODD number of ones in a word.

45
Q

Briefly explain the Command Word.(MIL-STD-1553)

A

1.Contain a terminal address which tells RT which component command is addressed to.
2. T/R prepares the RT to receive or transmit data.
3. Sub address mode memory location to transmit/store info.
4. Word count - How many data words are about to be sent to the RT or how many the RT must send back to BC.

46
Q

Briefly explain the Data word.(MIL-STD-1553)

A

Contains purely data and are always preceded by a command or status word to label what data is within.

47
Q

Briefly explain status word.(MIL-STD-1553)

A

Contains terminal address from where the status word is sent.

48
Q

Explain the transition of a signal,(MIL-STD-1553)

A

A Logic 0 = signal transitioning from negative to a positive level.
Logic 1 = signal transitioning from a positive to a negative level.

49
Q

The VOLTAGE levels on the bus are NOT the signaling media, how does it work?(MIL-STD-1553)

A

Its the timing and polarity of the ZERO crossings that convey information, the ramps up or down indicate a 0 or a 1, NOT the magnitude of voltage.

50
Q

BIT encoding for all words is based on? (MIL-STD-1553)

A

Bi-Phase Manchester 2 format.

51
Q

Why is the (MIL-STD-1553) so forgiving?

A

Forgiving of conditions that cause the voltage levels on the bus to vary.

52
Q

What are the 2 message format groups? (MIL-STD-1553)

A

Information transfer and broadcast information transfer.

53
Q

What does the remote terminal do upon validating the command and data word? (MIL-STD-1553)

A

Issues a status word indicating the message was received and was valid.

54
Q

What is the command/response philosophy?

A

Error free transmissions received by a RT are followed by the transmission of a STATUS WORD from the RT to the BC.

55
Q

BC to RT message is referred to as? BC-RC (MIL-STD-1553)

A

Receive command since the remote terminal is going to receive data.

56
Q

RT to BS is referred to as? (MIL-STD-1553)

A

Transmit command

57
Q

With the RT to RT command what are the RT’s called that send and receive data?(MIL-STD-1553)

A

RT - Data Source (sending data) to RT - Data Sink (Receiving data)

58
Q

On the (MIL-STD-1553) data can flow in?

A

Both directions it is bi-directional. means the bus MUST be managed by a BC

59
Q

What are the disadvantages of the (MIL-STD-1553)

A

Incorporated many A-D and D-A converters increasing cost of installs.

60
Q

What does the MIL-STD-1773 contain?

A

Requirements for utilizing fibre optic cabling as a transmission medium for the 1553 bus.

61
Q

What is the difference between 1553 and 1773?

A

Pulses are defines as transition between 0 (off) and 1 (on) rather than between + and - voltage transitions since light (fibre optics) cannot have a negative value.

62
Q

What considerations must be taken into account on 1773 system?

A

Environmental considerations for fibre optics (altitude, humidity, temperature.

Module 5 (10 decks)

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