General Questions Flashcards
What is Memory Mapping?
A device is assigned an address.
The address is used as if the device were an item of memory.
Values are written to or read from the device as if it were memory.
What are the trade-offs when selecting ADC?
The main trade off is between resolution and speed.
High resolution devices tend to be slower.
Very fast devices have poor resolution.
Another trade off is cost.
More expensive forms of ADC tend to be better.
What are the main forms of signal by which data can be taken in or out of a computer?
Digital Data. For example TTL.
Analogue Data. Varying voltage or current.
Trains of pulses. The rate form of digital data.
Describe Line Driver Digital Output.
A line driver is used to avoid spikes caused by interference.
Two signals are produced with complimentary lines.
One line goes up and the other goes down.
Both lines pick up the same spike due to common mode interference.
As a result the common mode interference is rejected.
What is Jitter?
Variation of actual loop cycle time from desired loop cycle time.
Even with real time operating systems, loop cycle time can vary between cycles.
What is Latency?
The time between input and output.
Describe Priority Inversion.
Consider three tasks with three varying levels of priority.
Priority inversion occurs when a high priority task is indirectly preempted by a low priority task.
This violates the priority model which states tasks can only be prevented from running by higher priority tasks.
What are the purposes of a counter timer?
Count based on the comparison of input signals.
To generate pulses based upon inputs and register values.
What are the main features of a counter timer?
Count register - stores the current count.
Source - Input signal that changes the current count. The active edge of the input signal changes the count.
Gate - Input signal that controls when counting occurs.
Out - Output signal used to generate pulses.
Why might a counter timer be used in preference to a simple, software-controlled digital I/O?
Timing is purely hardware-controlled and provides real-time response on a non real time system.
How can counter-timer circuit create a pulse train signal of frequency specified by software?
It requires a frequency divider.
Uses a hardware clock as a source.
Gives a pulse every time a given number of clock pulses has been received.
Output pulse rate is an integer fraction of clock pulse rate.
How can counter-timer circuit measure the frequency of a square signal wave?
Configure the counter timer as a counter.
Use it to count how many pulses are received in a 1second period.
The pulse would be received from another counter timer.
Converting from 5V(TTL) logic to 3.3V logic.
The outputs of the output device need to be fed into defined regions in the input device or results will be unpredictable.
If they provide an input voltage above the defined range, damage may occur.
A simple voltage divider and a logic level converter are needed.
What is totem-pole gate output?
Totem Pole is also known as Push-Pull.
Uses 2 transistor which act as switches to switch the output high or low.
What is Open Collector gate output?
Open collector only uses 1 transistor, together with a pull-up resistor, to connect to ground or leave it pulled up to some external voltage.
