48 Questions
Which type of keyboard has no hardware and must be analyzed by a software routine or by special hardware?
Non-encoded keyboard
What is the technique called that is used to detect a key press by outputting to the column lines with a 'walking zero' pattern and sensing the row lines to see if a low voltage is detected?
Row scanning
What is the main problem with keyboards that is caused by the fact that when the contacts of a mechanical switch close, they bounce for a short time before staying together?
Contact bouncing
What is the name of the technique used to prevent wrong codes from being generated when more than one key is held down at the same time?
N-key rollover
What is the name of the technique used to take into account only one key pressed, and any additional keys that might have been pressed and released do not generate any codes?
N-key lock-out
What is the name of the hardware device that is available to detect a key press without using processor-intensive process?
Keyboard controller
What is the name of the organization that is used for a larger number of keys, with an n by m key organization?
Matrix organization
What is the name of the cost-effective method used to assign each key to each buffer or port line for a small number of keys (1-8 keys)?
Direct connection
What is the name of the technique used to ignore the reading from the keyboard until only one key closure is detected?
Software n-key rollover
What is the name of the technique used to store all closures in an internal buffer if the order of keys pressed is not crucial?
Hardware n-key rollover
What is the name of the device that is needed to eliminate the problem created when three adjacent keys at a right angle are present when using n-key rollover protection?
Diode
What is the name of the technique used to prevent second and later key closures from generating a strobe until the earlier ones are released in n-key rollover protection?
Hardware n-key rollover
Which type of keyboard has no hardware and must be analyzed by a software routine or by special hardware?
Non-encoded keyboard
What is the technique called that is used to detect a key press by outputting to the column lines with a 'walking zero' pattern and sensing the row lines to see if a low voltage is detected?
Row scanning
What is the main problem with keyboards that is caused by the fact that when the contacts of a mechanical switch close, they bounce for a short time before staying together?
Contact bouncing
What is the name of the technique used to prevent wrong codes from being generated when more than one key is held down at the same time?
N-key rollover
What is the name of the technique used to take into account only one key pressed, and any additional keys that might have been pressed and released do not generate any codes?
N-key lock-out
What is the name of the hardware device that is available to detect a key press without using processor-intensive process?
Keyboard controller
What is the name of the organization that is used for a larger number of keys, with an n by m key organization?
Matrix organization
What is the name of the cost-effective method used to assign each key to each buffer or port line for a small number of keys (1-8 keys)?
Direct connection
What is the name of the technique used to ignore the reading from the keyboard until only one key closure is detected?
Software n-key rollover
What is the name of the technique used to store all closures in an internal buffer if the order of keys pressed is not crucial?
Hardware n-key rollover
What is the name of the device that is needed to eliminate the problem created when three adjacent keys at a right angle are present when using n-key rollover protection?
Diode
What is the name of the technique used to prevent second and later key closures from generating a strobe until the earlier ones are released in n-key rollover protection?
Hardware n-key rollover
Which type of keyboard requires a software routine or special hardware to analyze it?
Non-encoded keyboard
What is the technique used for scanning a keypad?
Row scanning
What is the most common problem with keyboards?
Contact bounce
What is the purpose of a dedicated keyboard controller hardware?
To detect key press
What is the technique used to prevent wrong codes from being generated when more than one key is held down at the same time?
N-key rollover
Which technique used to resolve the problem of multiple key presses stores all closures in an internal buffer if the order of keys pressed is not crucial?
N-key rollover
Which technique used to resolve the problem of multiple key presses takes into account only one key pressed, and any additional keys that might have been pressed and released do not generate any codes?
Hardware devices prevent second and later key closures from generating a strobe until the earlier ones are released
What is the technique used to scan a keyboard that has a large number of keys arranged in a row and column fashion?
Column scanning
What is the purpose of a diode in series with every key?
To eliminate the problem created when three adjacent keys at a right angle are present
What is the technique used to detect which key has been pressed in a keyboard?
Hardware and software
What is the technique used to read the keys in a keyboard that has a small number of keys (1-8 keys)?
Connected directly to a buffer or port to read the keys by checking for a low level
What is the main purpose of a keyboard?
To input information to microprocessors
Encoded keyboards have no hardware and must be analyzed by software routines or by special hardware.
False
Detecting a key press is a processor-intensive process that requires continually selecting a column line and then reading the row lines.
False
Row scanning is a technique used to detect a key press by outputting to the row lines with a 'walking zero' pattern and sensing the column lines to see if a low voltage is detected.
False
Non-encoded keyboards have no hardware and must be analyzed by a software routine or by special hardware.
True
For a small number of keys (1-8 keys), each key can be assigned to each buffer or port line, and the keyboard can be connected directly to a buffer or port to read the keys by checking for a high level.
False
Contact bounce refers to the fact that when the contacts of a mechanical switch close, they bounce for a long time before staying together.
False
N-key rollover is the technique used to ignore the reading from the keyboard until only one key closure is detected.
False
N-key lock-out takes into account all keys pressed and generates codes for all of them.
False
Most systems need a diode in series with every key to eliminate the problem created when three adjacent keys at a right angle are present with n-key rollover protection.
True
Hardware devices prevent second and later key closures from generating a strobe until the earlier ones are released in n-key lock-out.
False
Dedicated keyboard controller hardware is available, but it reduces product cost.
False
Scanning a keypad requires outputting to the row lines with a 'walking zero' pattern and sensing the column lines to see if a low voltage is detected, a technique known as 'column scanning'.
False
Study Notes
Keyboard Interfacing for Microprocessors
- A keyboard is a common method of input to microprocessors from humans, providing a low-cost way to input a large amount of information.
- A keyboard consists of pressure- or touch-activated switches arranged in a matrix, which requires a combination of hardware and/or software means to detect which key has been pressed.
- Two basic types of keyboards are available: encoded and non-encoded. Non-encoded keyboards have no hardware and must be analyzed by a software routine or by special hardware.
- For a small number of keys (1-8 keys), each key can be assigned to each buffer or port line, and the keyboard can be connected directly to a buffer or port to read the keys by checking for a low level.
- For a larger number of keys, the keyboard may be arranged in a row and column fashion, with an n by m key organization, also known as a matrix organization.
- Scanning a keypad requires outputting to the column lines with a "walking zero" pattern and sensing the row lines to see if a low voltage is detected, a technique known as "row scanning".
- Detecting a key press is a processor-intensive process that requires continually selecting a row line and then reading the column lines. Dedicated keyboard controller hardware is available, but it increases product cost.
- The most common problem with keyboards is contact bounce, which refers to the fact that when the contacts of a mechanical switch close, they bounce for a short time before staying together.
- When more than one key is held down at the same time, it is essential to detect this fact to prevent wrong codes from being generated. The two main techniques used to resolve this problem are the n-key rollover and the n-key lock-out.
- N-key rollover has two techniques: software ignores the reading from the keyboard until only one key closure is detected, or all closures are stored in an internal buffer if the order of keys pressed is not crucial. Hardware devices prevent second and later key closures from generating a strobe until the earlier ones are released.
- N-key lock-out takes into account only one key pressed, and any additional keys that might have been pressed and released do not generate any codes.
- A significant cost of n-key rollover protection is that most systems need a diode in series with every key to eliminate the problem created when three adjacent keys at a right angle are present. This increases the cost significantly and is seldom used on low-cost systems.
Keyboard Interfacing for Microprocessors
- A keyboard is a common method of input to microprocessors from humans, providing a low-cost way to input a large amount of information.
- A keyboard consists of pressure- or touch-activated switches arranged in a matrix, which requires a combination of hardware and/or software means to detect which key has been pressed.
- Two basic types of keyboards are available: encoded and non-encoded. Non-encoded keyboards have no hardware and must be analyzed by a software routine or by special hardware.
- For a small number of keys (1-8 keys), each key can be assigned to each buffer or port line, and the keyboard can be connected directly to a buffer or port to read the keys by checking for a low level.
- For a larger number of keys, the keyboard may be arranged in a row and column fashion, with an n by m key organization, also known as a matrix organization.
- Scanning a keypad requires outputting to the column lines with a "walking zero" pattern and sensing the row lines to see if a low voltage is detected, a technique known as "row scanning".
- Detecting a key press is a processor-intensive process that requires continually selecting a row line and then reading the column lines. Dedicated keyboard controller hardware is available, but it increases product cost.
- The most common problem with keyboards is contact bounce, which refers to the fact that when the contacts of a mechanical switch close, they bounce for a short time before staying together.
- When more than one key is held down at the same time, it is essential to detect this fact to prevent wrong codes from being generated. The two main techniques used to resolve this problem are the n-key rollover and the n-key lock-out.
- N-key rollover has two techniques: software ignores the reading from the keyboard until only one key closure is detected, or all closures are stored in an internal buffer if the order of keys pressed is not crucial. Hardware devices prevent second and later key closures from generating a strobe until the earlier ones are released.
- N-key lock-out takes into account only one key pressed, and any additional keys that might have been pressed and released do not generate any codes.
- A significant cost of n-key rollover protection is that most systems need a diode in series with every key to eliminate the problem created when three adjacent keys at a right angle are present. This increases the cost significantly and is seldom used on low-cost systems.
Test your knowledge of keyboard interfacing for microprocessors with our quiz! From understanding the basics of keyboard organization to detecting key press and dealing with contact bounce, this quiz will cover all the essential topics. Learn about the different types of keyboards and techniques used to prevent wrong codes from being generated when multiple keys are pressed at the same time. Improve your understanding of n-key rollover and lock-out and their impact on system cost. Take our quiz now and see how much you know about keyboard interfacing for
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