40 Questions
What is the primary purpose of heavily constructed power lines in electricity delivery grids?
To carry very high voltages and large electrical currents
Why does the starter motor in an aircraft require a thicker cable than the navigation light?
Because the starter motor draws a higher current
What is the primary advantage of using electricity for transmitting information?
It travels at the speed of light
What is the typical voltage of electrical signals transmitted over data bus lines?
5-V DC
What represents the data transmitted over digital data lines?
Series of 1s and 0s
What is the ideal current flow on a digital data line?
No current flow
What is the purpose of wiring in an aircraft starter motor?
To carry high currents efficiently
What is the purpose of electrical data transmission?
To transmit information
What is the ideal shape of a digital waveform?
Square wave
What voltage typically represents binary 0 in electronic digital systems?
0 V
What is the purpose of the clock pulse in serial data transfer?
To synchronize the transmitter and receiver
What is the primary advantage of serial data transfer over parallel data transfer?
Less hardware requirements
How is binary 1 typically represented in electronic digital systems?
By any voltage between 2 and 5 V
What is the primary difference between digital and analogue systems?
Digital systems have a wide voltage tolerance, while analogue systems require exact voltages
What is the purpose of the transmitter in serial data transfer?
To transmit data to the receiver
What is the term for the line on which data is transmitted sequentially in serial data transfer?
Serial bus
What was a major problem with the point-to-point analogue wiring system in aircraft?
It became increasingly complex and heavy
What was the main advantage of sharing sensors between systems?
It reduced the number of black boxes required by each system
What was the purpose of an Output Multiplier Box (OMB)?
To replicate analogue signals for output to multiple systems
What was a major limitation of analogue signals in avionics systems?
They required dedicated wiring
What was an advantage of digital technology in avionics systems?
It offered increased computational capability and easy growth
What is the primary function of a Bus Controller (BC) in a multiplexing system?
To manage all communications over the multiplexing bus
What is the benefit of multiplexing in avionics systems?
It reduces the amount of wiring required
What controls all data transmitted over the multiplexer buses?
The Flight Management Computer (FMC)
What is the primary advantage of parallel data transfer?
Increased data transfer speed
What is a major disadvantage of parallel data transfer?
It requires more hardware, which takes up space and increases weight
What is the main purpose of multiplexing in aircraft systems?
To decrease the number of wires carrying separate signals
How are analogue signals typically handled in aircraft multiplex systems?
They are converted to digital signals before transmission
What is the role of the Bus Controller (BC) in an aircraft multiplex system?
To receive and process inputs from multiple systems
What is the typical method of data transfer used in data-bus communications?
Serial data transfer
What is the benefit of using a 64-bit parallel bus compared to its equivalent serial bus?
It is 64 times faster
What was the characteristic of aviation electronics in the 1950s and 1960s?
They were simple stand-alone systems
What is the primary reason for using serial transmission of data in digital avionics systems?
To reduce the number of wires within the aircraft
What is the purpose of the twisted pair of wires in a digital data bus?
To reduce electromagnetic interference (EMI)
What controls the transmission of data on a digital data bus?
The Bus Controller (BC)
What is the function of a Bus Controller (BC) in a digital avionics system?
To manage data transmission and request data from peripheral components
What type of data transmission is used in digital avionics systems?
Both simplex and duplex transmission
What is the purpose of the shielding on the digital data bus wires?
To eliminate electromagnetic interference (EMI)
What is the role of the multiplexer bus in a digital avionics system?
To function as an arterial highway for data transmission
How many data words are transmitted on the digital data bus at any given time?
One data word
Study Notes
Data Transmission and Electrical Power
- Electricity is used to transmit signals, and ideally, no current flows on a digital data line.
- In reality, a small flow of current is sufficient to forward and reverse bias semiconductor P and N junctions.
- Data bus lines are typically small gauge, and the electrical signal transmitted over them is typically no higher than 5-V DC.
Digital Data Transfer
- An ideal digital waveform is a square wave, but in reality, it is more like a distorted AC sine wave.
- The voltage produced is a result of the transistor switching ON and OFF.
- Transistors are not perfect in respect to instantaneously switching states from OFF to fully saturated.
Ideal vs Practical Digital Signal
- In electronic digital systems, data in binary form is represented by the presence or lack of a voltage for each bit at the inputs and outputs of the various circuits.
- Typically, binary 0 is represented by 0 V, and binary 1 is represented by 5 V.
- In practical systems, any voltage between 0 and 0.8 V represents binary 0, and any voltage between 2 and 5 V represents a binary 1.
Serial Data Transfer
- Serial data transfer is typical of data-bus communications.
- In serial transfer, each bit of data is transferred from a store (or memory location) in sequence over the same line.
- The data is triggered by clock pulses, and the transmitter and receiver are synchronised with reference to the same clock pulse.
Parallel Data Transfer
- In parallel transfer, each bit is taken from a separate circuit and is transmitted over a separate line.
- Advantage of parallel data transfer: much faster.
- In the example, it would be 16 times faster than serial data transfer.
Multiplexing
- Multiplexing is combining two or more information channels onto a common transmission medium.
- Benefits include a significant reduction in the weight of wire bundles and improved circuit reliability.
- Multiplexing is typically done by logic gates responding in sequence to clock pulse signals.
Aircraft Multiplex System
- In an aircraft, the sequencing controller is replaced by a Bus Controller (BC), which typically receives all the inputs and distributes outputs and processed data to systems requiring the information.
- The BC works similarly to a base station radio operator.
- The mission computers control all data transmitted over the multiplexer buses.
Data Bus Systems
- The interface between each computer and external device is accomplished via the digital data bus.
- The bus is made up of a twisted pair of wires which are shielded and jacketed.
- Data may travel one way (simplex) or in two directions (duplex), depending on the system design.
Data Bus Connectors
- The multiplexer bus functions like an arterial highway and is not designed to connect to any specific components.
- All the peripheral components are connected to the highway by breakouts (couplers) and perform similarly to telephone extensions connected to an exchange or computers connected to a Local Area Network (LAN).
Bus Controller
- The Bus Controller (BC) manages all data transmitted over the multiplexing bus.
- The BC is the only one allowed to issue commands on the data bus.
- Commands may be for the transfer of data or control and management of the bus.
- The BC sends out commands to peripheral systems requesting data stored in the memory of the peripheral components.
Data bus transmition theory
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