Programmable Interfacing Devices Quiz
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Questions and Answers

What is a primary function of the Programmable Peripheral Interface 8255?

  • To serve as a memory module
  • To interface the CPU with external devices (correct)
  • To manage power supply to the CPU
  • To perform arithmetic calculations

    • Which of the following ports can be configured as an input function in Mode 0?

  • None of the ports can be configured in Mode 0
  • Only PORT B
  • All three ports: PORT A, PORT B, and PORT C (correct)
  • Only PORT A

    • Which mode allows the use of only port C bits for set or reset operations?

  • Bit Set Reset (BSR) mode (correct)
  • Mode 1
  • Input-Output mode
  • Mode 0

    • Which control group of the PPI 8255 contains PORT A?

    <p>Control Group A</p> Signup and view all the answers

    What is the purpose of the control register in PPI 8255?

    <p>To configure the operational mode and port functions</p> Signup and view all the answers

    What voltage does the PPI 8255 operate on?

    <p>+5V</p> Signup and view all the answers

    In what mode does PPI 8255 have no interrupt handling capacity?

    <p>Mode 0</p> Signup and view all the answers

    Which pins are used for data transfer in the PPI 8255?

    <p>D0 - D7</p> Signup and view all the answers

    What is the primary function of port C in the PPI 8255?

    <p>Handshake signals for synchronization</p> Signup and view all the answers

    Which mode allows for handshake signals using all three ports of the PPI 8255?

    <p>Mode 1</p> Signup and view all the answers

    What occurs when the most significant bit (MSB) of the control word in the PPI 8255 is set to 0?

    <p>The device operates in Bit Set-Reset (BSR) mode</p> Signup and view all the answers

    What is one of the major disadvantages of the PPI 8255?

    <p>Limited memory capacity</p> Signup and view all the answers

    How many ports are provided by the PPI 8255?

    <p>3 8-bit ports</p> Signup and view all the answers

    Which mode of the PPI 8255 allows only one port to work, while the other can operate in a different mode?

    <p>Mode 2</p> Signup and view all the answers

    Which application is a common use for the PPI 8255?

    <p>Traffic light control</p> Signup and view all the answers

    What is a key benefit of programming the PPI 8255?

    <p>It allows versatile I/O operations</p> Signup and view all the answers

    In which scenario would the PPI 8255 most likely be hindered by its limited resolution?

    <p>Interfacing with complex sensors</p> Signup and view all the answers

    What describes the I/O mode of the PPI 8255 when the MSB of the control word is set to 1?

    <p>Input-output capabilities are enabled</p> Signup and view all the answers

    What challenge does using the PPI 8255 add to system complexity?

    <p>Involves extensive coding and programming knowledge</p> Signup and view all the answers

    What is the significance of the control register in the PPI 8255?

    <p>It controls the operational mode of each port</p> Signup and view all the answers

    What is a major limitation of the PPI 8255 related to newer technology?

    <p>It lacks modern functionality and higher data transfer speeds</p> Signup and view all the answers

    What is necessary for communicating with peripherals through the PPI 8255?

    <p>writing a control word in the control register</p> Signup and view all the answers

    What is one of the disadvantages of the 8251 USART?

    <p>Has a small internal buffer size</p> Signup and view all the answers

    Which feature differentiates the 8254 from the 8253?

    <p>Availability of Read-Back command</p> Signup and view all the answers

    What is a key feature of the 8253 and 8254 Programmable Interval Timers?

    <p>They can handle inputs from DC to 10 MHz</p> Signup and view all the answers

    Which of the following statements best describes the function of the control word register in the 8253/54?

    <p>It specifies the counter mode and operation type</p> Signup and view all the answers

    Which of these operating frequencies is associated with the 8253?

    <p>0 - 2.6 MHz</p> Signup and view all the answers

    What is one challenge when programming the 8251 USART?

    <p>Requires careful attention to timing parameters</p> Signup and view all the answers

    What is the maximum data transfer rate of the 8251 USART?

    <p>115.2 kbps</p> Signup and view all the answers

    How many counters does the 8253 and 8254 have?

    <p>Three independent 16-bit counters</p> Signup and view all the answers

    What does the control register of 8253/54 primarily do?

    <p>It selects the counter for operations</p> Signup and view all the answers

    Which factor contributes to the cost of incorporating 8251 USART in a system?

    <p>Need for multiple USARTs in some applications</p> Signup and view all the answers

    What is one of the main limitations of the 8255 PPI?

    <p>It provides only three 8-bit ports.</p> Signup and view all the answers

    How many interrupt lines can be handled by cascading additional 8259 chips?

    <p>64 lines</p> Signup and view all the answers

    What primary function does the 8251 USART perform?

    <p>Transmit serial data to peripheral and vice versa.</p> Signup and view all the answers

    Which of the following correctly describes the function of the Data Bus Buffer in the 8259?

    <p>It communicates between the 8259 and the microprocessor.</p> Signup and view all the answers

    What is a feature of the 8259 Programmable Interrupt Controller?

    <p>It can operate in edge-triggered or level-triggered mode.</p> Signup and view all the answers

    What does the Control Logic block of the 8259 handle?

    <p>Determination of interrupt priority.</p> Signup and view all the answers

    In USART operation, what signal indicates that the transmitter is ready to transmit data?

    <p>TXRDY</p> Signup and view all the answers

    What is one advantage of using the 8251 USART?

    <p>It includes built-in error detection features.</p> Signup and view all the answers

    Which block in the 8259 is responsible for storing interrupt requests?

    <p>Interrupt Request Register</p> Signup and view all the answers

    What is the primary role of the Interrupt Mask Register in the 8259?

    <p>To select which interrupts to allow or block.</p> Signup and view all the answers

    What does the 'Transmit Buffer' in the 8251 USART do?

    <p>Holds parallel data for conversion to serial.</p> Signup and view all the answers

    Which signal indicates that no data characters are available for transmission in the TXEMPTY pin?

    <p>It is set to high.</p> Signup and view all the answers

    What main problem does the 8255 PPI face in modern applications?

    <p>It is considered obsolete technology.</p> Signup and view all the answers

    Which port configuration allows for BSR mode operations in the PPI 8255?

    <p>Port C</p> Signup and view all the answers

    What is the maximum number of ports that can operate in input-output mode simultaneously in PPI 8255?

    <p>Three ports</p> Signup and view all the answers

    What is indicated by the value of control bits A1 and A0 in the PPI 8255?

    <p>Port selection</p> Signup and view all the answers

    Which function does Mode 1 of input-output operations provide for the PPI 8255?

    <p>Handshake I/O operations</p> Signup and view all the answers

    Which of the following is not a feature of the PPI 8255?

    <p>Automatic data handling</p> Signup and view all the answers

    In which situation would Port B of the PPI 8255 typically operate in mode 1?

    <p>When handshake signals are required</p> Signup and view all the answers

    What configuration of the PPI 8255 would be used to prevent any port selection?

    <p>1 X X</p> Signup and view all the answers

    What type of signals is Port C of the PPI 8255 capable of handling when configured in BSR mode?

    <p>Set or reset signals</p> Signup and view all the answers

    What is a disadvantage of the PPI 8255 regarding its ports?

    <p>It provides only three 8-bit ports.</p> Signup and view all the answers

    What is the primary function of handshake signals in PPI 8255 operation?

    <p>To synchronize the CPU with peripherals.</p> Signup and view all the answers

    How many bits are used in Port C for handshake signals in the PPI 8255?

    <p>6 bits</p> Signup and view all the answers

    Which mode of the PPI 8255 does not support interrupt handling capabilities?

    <p>Mode 0</p> Signup and view all the answers

    What happens when the most significant bit (MSB) of the control word in the PPI 8255 is set to 1?

    <p>The PPI operates in Input-Output mode.</p> Signup and view all the answers

    What is one reason the PPI 8255 is considered obsolete technology?

    <p>It is being replaced by newer I/O interface components.</p> Signup and view all the answers

    Why might the PPI 8255 add complexity to a system?

    <p>It needs specific programming to manage data transfer.</p> Signup and view all the answers

    Which application is NOT commonly associated with the PPI 8255?

    <p>Graphical user interface rendering</p> Signup and view all the answers

    In which mode does the PPI 8255 implement only port C for set and reset operations?

    <p>Bit Set Reset (BSR) mode</p> Signup and view all the answers

    What makes the PPI 8255 a versatile component?

    <p>It can be programmed for various input/output modes.</p> Signup and view all the answers

    Which of the following statements about the control register in the PPI 8255 is true?

    <p>It specifies I/O functions for each port.</p> Signup and view all the answers

    What is one of the features that differentiate the I/O mode from the BSR mode in the PPI 8255?

    <p>I/O mode uses interrupt handling capabilities but BSR does not.</p> Signup and view all the answers

    Which characteristic of the PPI 8255 is a significant limitation when compared to newer technologies?

    <p>Limited memory capacity and functionality</p> Signup and view all the answers

    What must occur first before actual data transmission can take place in PPI 8255 operations?

    <p>Data must be written to the control register first.</p> Signup and view all the answers

    What is a significant disadvantage of the 8251 USART regarding data handling?

    <p>It has a small internal buffer size.</p> Signup and view all the answers

    What feature distinguishes the 8254 from the 8253?

    <p>It offers a Read-Back command.</p> Signup and view all the answers

    When using the Read/Write logic of the 8253/54, what signal combination is required to read Counter 1?

    <p>A1: 0, A0: 1, RD: 1, WR: 0</p> Signup and view all the answers

    What operational frequency range is associated with the 8253?

    <p>0 - 2.6 MHz</p> Signup and view all the answers

    What is a common programming challenge faced when using the 8251 USART?

    <p>Timing parameters must be managed carefully.</p> Signup and view all the answers

    Which feature is NOT part of the architecture of the 8254?

    <p>Supports only binary count modes.</p> Signup and view all the answers

    What signal combination in the control word register of the 8253/54 allows writing to Counter 2?

    <p>A1: 1, A0: 0, RD: 0, WR: 0</p> Signup and view all the answers

    Which of the following describes a limitation of using the 8251 USART in some applications?

    <p>Limited maximum data transfer rate.</p> Signup and view all the answers

    What is a significant characteristic of the Data Bus Buffer in the 8253/54?

    <p>It is used for programming modes and reading counts.</p> Signup and view all the answers

    Which of the following disadvantages is associated with the use of the 8251 USART?

    <p>Complexities in its programming.</p> Signup and view all the answers

    What is one of the key limitations of the 8255 PPI in modern applications?

    <p>Limited number of ports</p> Signup and view all the answers

    How does the 8259 Programmable Interrupt Controller enhance interrupt handling?

    <p>Increases the number of interrupt lines via cascading</p> Signup and view all the answers

    What feature of the 8251 USART allows it to communicate both synchronously and asynchronously?

    <p>Versatile operation modes</p> Signup and view all the answers

    Which component in the 8259 is responsible for determining the priority of interrupts?

    <p>Priority Resolver</p> Signup and view all the answers

    What does the Receive Control block in the 8251 USART primarily do?

    <p>Buffers incoming serial data</p> Signup and view all the answers

    In what mode can the 8259 PIC program its interrupts?

    <p>Both edge-triggered and level-triggered modes</p> Signup and view all the answers

    What function does the Read/Write Control Logic in the 8259 serve?

    <p>Transfers control words from the CPU</p> Signup and view all the answers

    What does the TXRDY signal in the 8251 USART indicate?

    <p>The transmitter is ready to send data</p> Signup and view all the answers

    Which block in 8251 USART aids in data conversion between formats?

    <p>Transmit Buffer</p> Signup and view all the answers

    How many hardware interrupts are available in the 8086 microprocessor without the 8259?

    <p>Five</p> Signup and view all the answers

    Which register in the 8259 is used to mask individual interrupts?

    <p>Interrupt Mask Register</p> Signup and view all the answers

    What kind of signal does the RTS pin in the modem control of the 8251 USART represent?

    <p>Request to Send</p> Signup and view all the answers

    What happens when the interrupt request with the highest priority is serviced in the 8259?

    <p>It is stored in the Interrupt Service Register</p> Signup and view all the answers

    What characterizes the versatility of the 8251 USART?

    <p>Acts as a bridge for parallel and serial data</p> Signup and view all the answers

    Study Notes

    Programmable Interfacing Devices

    • Programmable interfacing devices are essential components in microprocessor-based systems, enabling communication between the CPU and the outside world.
    • These devices allow for flexible and efficient data transfer, handling various types of peripherals and controlling their functionality.

    Programmable Peripheral Interface (PPI) 8255

    • The PPI 8255 is a versatile I/O device commonly used to interface the CPU with peripherals like ADCs, DACs, keyboards, etc.
    • It consists of three 8-bit bidirectional ports: Port A, Port B, and Port C.
    • Each port can be programmed as either input or output, providing flexibility in connecting different peripherals.

    Internal Architecture

    • The 8255 has a control register that allows the user to select the mode of operation for each port.
    • The control register is accessed by using specific address combinations (CS', A1, A0) to select the desired port.
    • Depending on the control word (D0 - D7), the ports can be configured for various functions, including basic input/output, handshake operations, and bi-directional data bus mode.

    Operating Modes:

    • Bit Set Reset (BSR) Mode: Port C bits are used to set or reset individual pins, providing basic control for external devices.
    • Input-Output Mode: This mode allows for more complex data transfer, including interrupt handling capabilities.
      • Mode 0: All three ports (A, B, and C) can operate as simple input or output ports.
      • Mode 1: This is a handshake I/O mode where either Port A or Port B can operate as input or output, and Port C bits are used for handshake signals to synchronize data transfer.
      • Mode 2: This mode is for bi-directional data transfer, where only Port A operates, and Port B can be in Mode 0 or Mode 1. Port C is used for handshake signals, providing interrupt support.

    Advantages

    • Versatility: The PPI 8255 can be programmed to operate in various modes, making it suitable for various applications.
    • Ease of use: Programming the PPI 8255 is relatively straightforward, even for novice programmers.
    • Compatibility: Its widespread use and long history ensure compatibility with a wide range of microprocessors and software.
    • Low cost: The PPI 8255 is an affordable option for many applications.

    Disadvantages

    • Limited functionality: Compared to newer I/O interface components, the PPI 8255 has limited capabilities in terms of data transfer speed and memory capacity.
    • Limited number of ports: The three 8-bit ports provided may not be sufficient for systems with complex I/O requirements.
    • Limited resolution: The 8-bit resolution may not be suitable for applications demanding higher accuracy.
    • Obsolete technology: While still used in some systems, the PPI 8255 is considered an older technology and is being replaced by newer alternatives.

    Programmable Interrupt Controller (PIC) 8259

    • The 8259 PIC is a crucial component that expands the interrupt handling capabilities of a microprocessor system.
    • It can manage multiple interrupt requests from various external devices and prioritize them before sending a single interrupt signal to the CPU.

    Internal Architecture

    • The 8259 consists of multiple internal registers:
      • Interrupt Request Register (IRR): Stores the interrupt levels requesting service.
      • Interrupt Service Register (ISR): Contains the interrupt level currently being serviced.
      • Interrupt Mask Register (IMR): Allows for selective masking of interrupts, disabling specific interrupt levels.
    • The 8259 includes a priority resolver that determines the highest-priority interrupt based on the contents of these registers, prioritizing interrupt service.

    Features:

    • The 8259 is designed to work with the Intel 8085 and 8086 microprocessors.
    • It supports edge-triggered and level-triggered interrupt modes.
    • The 8259 allows for masking individual interrupt requests, providing flexibility in managing interrupts.
    • Multiple 8259 chips can be cascaded to manage a larger number of interrupts (up to 64 lines).

    Advantages:

    • Interrupt management: The 8259 enables effective management of multiple interrupt requests, ensuring efficient handling of external events.
    • Priority handling: It prioritizes interrupts based on their importance, ensuring that critical tasks are handled promptly.
    • Flexibility: The 8259 can be configured to accommodate various interrupt sources and handle them according to specific needs.

    Disadvantages:

    • Complexity: Programming and configuring the 8259 can be somewhat complex, requiring understanding of its internal registers and operation.
    • Limited scalability: While cascading multiple 8259s allows for greater capacity, the number of interrupts is limited compared to modern interrupt controllers.
    • Legacy technology: The 8259 is considered legacy technology, and newer interrupt controllers offer more features and better performance.

    Universal Synchronous Asynchronous Receiver Transmitter (USART) 8251

    • The 8251 USART acts as a communication interface between the CPU and serial peripherals, converting parallel data from the CPU into serial data for transmission and vice versa.

    Internal Architecture:

    • The 8251 includes:
      • Data bus buffer: Handles communication between the 8251's internal data bus and the system data bus.
      • Read/Write control logic: Controls the overall operation of the USART by selecting the register to be accessed (data buffer, control, or status).
      • Modem control: Provides control signals for communication over phone lines or cable wires, including DSR, DTR, CTS, and RTS.
      • Transmit buffer: Converts parallel data into serial data, transmitting it via the TXD pin.
      • Transmit control: Handles the control of data transmission, including signals like TXRDY (transmitter ready), TXEMPTY (transmitter empty), and TXC (transmit clock).
      • Receive buffer: Temporarily stores received serial data until it can be read by the CPU.
      • Receive control: Controls data reception, providing signals like RXRDY (receiver ready) and RXC (receive clock).

    Advantages:

    • Versatility: The 8251 can handle both synchronous and asynchronous communication, making it adaptable to different protocols.
    • Error detection: The 8251 includes error detection mechanisms like parity checking, ensuring data accuracy.
    • Flow control: It supports flow control, regulating data transmission and reception, preventing data loss.
    • Compatibility: The 8251 is compatible with a wide range of microprocessors, making it a popular choice for serial communication.
    • Ease of use: The 8251's interface pins and registers are relatively simple.

    Disadvantages:

    • Limited speed: Compared to newer communication interfaces the 8251's maximum data transfer rate is relatively low.
    • Limited buffer size: The small internal buffer size can lead to data loss if the data is not read quickly enough.
    • Complex programming: Programming the 8251 involves careful consideration of timing and other parameters, which can be complex.
    • Cost: While relatively affordable, the 8251 adds cost to a system, especially if multiple USARTs are required.
    • Limited functionality: Compared to modern communication interfaces, the 8251 lacks advanced features.

    Programmable Interval Timer (PIT) 8253/8254

    • The 8253 and 8254 are programmable interval timers designed to provide timing and counting functions in microprocessor systems.
    • They consist of three independent 16-bit counters that can be programmed for various timing and counting applications.

    Internal Architecture:

    • The 8253/8254 consists of:
      • Three 16-bit counters: Each counter can be programmed independently for various modes of operation.
      • Data bus buffer: A tri-state buffer that handles communication with the system data bus.
      • Read/Write control logic: Controls the selection and operation of the counters.
      • Control word register: Stores the control word that specifies counter operation, including mode, read/write operation, and other parameters.

    Features:

    • Supports a wide range of frequencies, from DC to 10 MHz.
    • Allows for binary or BCD counting.
    • Provides counter reset and latch functions.
    • The 8254 includes a "Read Back" command, allowing access to the current counter value, programmed mode, and status.

    Advantages:

    • Timing and counting: The 8253/8254 provides accurate timing and counting capabilities, enabling precise timing functions in microprocessor systems.
    • Versatility: The programmable counters offer flexibility, allowing for various timing and counting applications.
    • Compatibility: The 8253/8254 are compatible with a wide range of microprocessors, providing a widely used timing solution.

    Disadvantages:

    • Limited number of counters: Each 8253/8254 chip provides only three counters, potentially limiting complex timing applications.
    • Legacy technology: These devices are considered legacy technology, and newer timer chips offer more advanced capabilities.

    Programmable Peripheral Interface (PPI) 8255

    • The PPI 8255 is a general purpose programmable input/output (I/O) device that enables connection between a CPU and various peripherals, such as analog-to-digital converters (ADCs), digital-to-analog converters (DACs), and keyboards.

    • It offers three 8-bit bidirectional I/O ports (Port A, Port B, and Port C), allowing users to configure different ports as input or output functions.

    • Port C can function as a bit set/reset (BSR) mode or in the input/output (I/O) mode.

    • It has two control groups (Control Group A and Control Group B), facilitating different port combinations in various modes.

    • The 8255 operates using a +5V regulated power supply and possesses 40 pins.

    • The device's functionality depends on the configuration of the control register (Control Word D0-D7) which dictates the operation of the ports.

    Programmable Interrupt Controller (PIC) 8259

    • The 8259 PIC is a programmable interrupt controller designed to enhance the interrupt handling capabilities of microprocessors like the 8085 and 8086.

    • It enables the CPU to handle multiple interrupts simultaneously by combining multiple interrupt input sources into a single interrupt output.

    • The 8259 can handle up to 8 interrupts (IR0 to IR7) and can be configured for edge-triggered or level-triggered modes.

    • Individual interrupt requests can be masked using the Interrupt Request Register (IRR), and the interrupt priority is determined by the Priority Resolver.

    • The 8259 can be cascaded with other 8259 chips to increase the interrupt capacity to 64 interrupts.

    Universal Synchronous Asynchronous Receiver Transmitter (USART) 8251

    • The USART 8251 facilitates communication between a microprocessor and peripherals by converting serial data into parallel format and vice versa.

    • It receives serial data from peripherals and transmits it to the CPU after converting it to parallel form.

    • Conversely, it receives parallel data from the CPU and converts it to serial form before transmitting it to external devices.

    • The 8251 has distinct blocks for data transmission and reception: Data Bus Buffer, Read/Write control logic, Modem control, Transmit buffer, Transmit control, Receive buffer, and Receive control.

    Programmable Interval Timer (PIT) 8253/8254

    • The 8253/8254 is a Programmable Interval Timer (PIT) that leverages three 16-bit registers to execute timing and counting functions.

    • Each counter comprises two input pins: Clock and Gate, and one output pin: OUT.

    • To operate a counter, a 16-bit count value is loaded into its register. The counter decrements the count until it reaches zero and generates a pulse that can interrupt the CPU.

    • The 8253 and 8254 have distinct operating frequencies, and the 8254 offers a "READ BACK" command for checking the count value, programmed mode, and status of the counter.

    • Each counter in the 8253/8254 can be independently programmed for either a binary or BCD count. The device is compatible with various microprocessors.

    8254 Architecture Overview

    • The 8254 architecture consists of three counters (Counter 0, Counter 1, Counter 2), a data bus buffer, Read/Write control logic, and a Control Word Register.

    • The data bus buffer acts as a tri-state, bi-directional, 8-bit buffer for communication with the system data bus.

    • The Read/Write control logic utilizes signals like RD, WR, CS, and address lines A0 and A1 for data control.

    • The Control Word Register is addressed using A0 and A1 when both are set to logic 1 and is used to write a command word that specifies the counter being used, its mode, and whether a read or write operation is being performed.

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    Test your knowledge on programmable interfacing devices and the PPI 8255. This quiz covers essential concepts, the internal architecture of the PPI 8255, and its role in microprocessor systems. Great for students studying computer architecture and interfacing!

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