Programmable Peripheral Interface 8255 Quiz
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Questions and Answers

What is the primary purpose of the Programmable Peripheral Interface (PPI) 8255?

  • To manage memory allocation for the CPU
  • To regulate power supply to microprocessors
  • To interface the CPU with external devices (correct)
  • To provide a direct connection to storage devices

    • Which ports of the PPI 8255 can be assigned input or output functions?

  • Only PORT A
  • PORT A, PORT B, and PORT C (correct)
  • Only PORT C
  • PORT A and PORT C

    • In which mode does the PPI 8255 support handshake I/O operations?

  • Mode 0
  • BSR mode
  • Mode 2
  • Mode 1 (correct)

    • What does the Control Register of the PPI 8255 do?

    <p>It allows selection of operating modes for the ports</p> Signup and view all the answers

    Which pin mode does Port C operate in when configured for BSR mode?

    <p>Only Port C bits are used for set or reset</p> Signup and view all the answers

    How many bits are there in each of the I/O ports of the PPI 8255?

    <p>8 bits</p> Signup and view all the answers

    Which component of the PPI 8255 allows for selecting different ports?

    <p>Address pins A1 and A0</p> Signup and view all the answers

    What happens to the PPI 8255 input-output operations in Mode 0?

    <p>All ports operate as simple input or output</p> Signup and view all the answers

    What is the primary function of the 8255 PPI?

    <p>To provide parallel I/O ports</p> Signup and view all the answers

    How many interrupt lines can be achieved by cascading 8259 chips?

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

    What role does the Data Bus Buffer play in the operation of the 8259?

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

    Which feature of the 8259 allows for the masking of individual interrupt requests?

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

    What is the maximum amount of data the Data Bus Buffer of the 8259 can send at one time?

    <p>8 bits</p> Signup and view all the answers

    What additional feature does 8251 USART provide for communication?

    <p>Error detection mechanisms</p> Signup and view all the answers

    In the context of the 8251 USART, what does TXRDY signify?

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

    What type of communication does 8251 USART facilitate?

    <p>Both synchronous and asynchronous communication</p> Signup and view all the answers

    What is a primary disadvantage of the 8255 PPI?

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

    Which component controls the overall working of the 8251?

    <p>Read/Write Control Logic</p> Signup and view all the answers

    What is the function of the Priority Resolver in the 8259?

    <p>To check, store, and set the priority of interrupts</p> Signup and view all the answers

    What signals are controlled by the RTS pin in the modem control block of the 8251?

    <p>Status of data transmission circuits</p> Signup and view all the answers

    How is the 8251 USART primarily utilized?

    <p>To convert data between serial and parallel formats</p> Signup and view all the answers

    What does the Interrupt Request Register in the 8259 serve to do?

    <p>Store interrupt levels requesting service</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

    Which of the following is a disadvantage of the 8251 USART?

    <p>Small internal buffer size</p> Signup and view all the answers

    What technology is used in the 8253 chip?

    <p>N-MOS technology</p> Signup and view all the answers

    Which command is unique to the 8254 compared to the 8253?

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

    How many independent 16-bit counters does the 8253/54 have?

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

    Which signal is NOT used in the Read/Write logic of the 8253/54?

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

    What is the main function of the data bus buffer in the 8253/54 architecture?

    <p>Interfacing with the system data bus</p> Signup and view all the answers

    In the 8253/54 architecture, what does the 'OUT' pin signify?

    <p>Generated pulse for interruption</p> Signup and view all the answers

    What is the operating frequency range of the 8254?

    <p>0 - 10 MHz</p> Signup and view all the answers

    Which of the following is a limitation of the 8251 USART regarding memory access?

    <p>It has complex programming requirements.</p> Signup and view all the answers

    Which mode of the PPI 8255 allows only port A to operate?

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

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

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

    What happens when the most significant bit of the control word is set to 0?

    <p>It operates in BSR mode.</p> Signup and view all the answers

    Which of the following is NOT a disadvantage of the PPI 8255?

    <p>Low compatibility</p> Signup and view all the answers

    What advantage does the PPI 8255 provide concerning system performance?

    <p>Offloads I/O operations from the CPU</p> Signup and view all the answers

    How many bits does each port of the PPI 8255 provide?

    <p>8 bits</p> Signup and view all the answers

    In which mode does the PPI 8255 not support interrupt handling capabilities?

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

    Which of the following is a common application of the PPI 8255?

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

    What is one of the benefits of the PPI 8255's programmability?

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

    What is the primary limitation of the PPI 8255 in terms of I/O capabilities?

    <p>Only has three 8-bit ports</p> Signup and view all the answers

    Which of the following characteristics relates to the PPI 8255 regarding its operational modes?

    <p>Variability of operation modes enhances versatility</p> Signup and view all the answers

    Which port configuration allows for the highest efficiency in data transfer?

    <p>Port A in Mode 2 and Port B in Mode 0 or 1</p> Signup and view all the answers

    What is a characteristic of the control register in the 8255?

    <p>Specifies I/O function for each port</p> Signup and view all the answers

    Which component does the PPI 8255 primarily interface with for I/O operations?

    <p>Peripheral devices</p> Signup and view all the answers

    Which mode of the PPI 8255 restricts the operation to simple input or output functions without any interrupt handling?

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

    What is the function of port C in the PPI 8255 when configured to operate in BSR mode?

    <p>To set or reset bits</p> Signup and view all the answers

    What is the maximum number of bits that can be configured in port C of the PPI 8255?

    <p>4 bits</p> Signup and view all the answers

    Which control word setting indicates that the PPI 8255 should operate in input-output mode?

    <p>MSB (D7) = 1</p> Signup and view all the answers

    Which of the following pins is NOT used in the operation of the PPI 8255?

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

    In which mode does Port B of the PPI 8255 operate when it is configured for input-output functions?

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

    What happens to the PPI 8255 when the most significant bit of the control word is set to 0?

    <p>It operates in BSR mode.</p> Signup and view all the answers

    Which address is assigned to the control register of the PPI 8255?

    <p>83H</p> Signup and view all the answers

    Which disadvantage is associated with the 8251 USART regarding its data transmission capabilities?

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

    What is the operating frequency range for the 8253 chip?

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

    Which feature is unique to the 8254 compared to the 8253?

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

    Which aspect of the 8251 USART contributes to its complexity in programming?

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

    What is one of the capabilities of the data bus buffer in the 8253/54 architecture?

    <p>It is used to program the modes of 8253/54.</p> Signup and view all the answers

    What advantage does the 8254 have over the 8253 regarding counter operations?

    <p>Ability to read and write the same counter interleaved.</p> Signup and view all the answers

    Which of these features makes the 8251 USART particularly suitable for various systems?

    <p>Compatibility with a wide range of microprocessors.</p> Signup and view all the answers

    How many independent 16-bit down counters do the 8253 and 8254 provide?

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

    What is a primary limitation of the 8251 USART regarding data transfer speed?

    <p>Limited data transfer rate of 115.2 kbps.</p> Signup and view all the answers

    What type of technology is utilized in the 8253?

    <p>N-MOS technology</p> Signup and view all the answers

    What is a key feature of the 8259 Programmable Interrupt Controller?

    <p>It provides 8 interrupt lines from IR0 to IR7.</p> Signup and view all the answers

    Which block in the 8259 is responsible for storing currently executing interrupt levels?

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

    What process does the 8251 USART perform when receiving data?

    <p>Transforms serial data into parallel form.</p> Signup and view all the answers

    Which register in the 8259 allows for the individual masking of interrupt requests?

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

    What characteristic of the Priority Resolver in the 8259 determines which interrupts are processed first?

    <p>It sets the highest priority interrupt in the ISR register.</p> Signup and view all the answers

    Which component in the 8251 USART controls the overall functioning of the device?

    <p>Read/Write control logic</p> Signup and view all the answers

    What type of signals does the RTS pin in the modem control block of the 8251 represent?

    <p>Request to send data status.</p> Signup and view all the answers

    What is one significant limitation of the 8255 PPI regarding peripheral interface?

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

    In cascading 8259 chips, what advantage does this provide?

    <p>It allows for an increase of interrupts up to 64 lines.</p> Signup and view all the answers

    Which of the following roles is performed by the Transmit Buffer in the 8251 USART?

    <p>To convert parallel data to serial data.</p> Signup and view all the answers

    What is a notable advantage of the 8251 USART?

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

    What is the primary function of Data Bus Buffer in the 8259?

    <p>To facilitate data transfer between microprocessors.</p> Signup and view all the answers

    Which operation does the 8251 USART NOT perform in its data handling capabilities?

    <p>Store data for future processing.</p> Signup and view all the answers

    What function does the Control Logic in the 8259 serve?

    <p>To respond to interrupt requests.</p> Signup and view all the answers

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

    <p>To serve as a control signal for handshake operations</p> Signup and view all the answers

    In I/O mode, what is the capability provided by mode 1 of the PPI 8255?

    <p>Utilizes handshake signals and supports interrupt handling</p> Signup and view all the answers

    What determines the operational mode of the PPI 8255?

    <p>The value of the control word's most significant bit</p> Signup and view all the answers

    Which mode of the PPI 8255 allows for only port A to operate effectively?

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

    What is one major disadvantage of using the PPI 8255?

    <p>It provides limited memory capacity</p> Signup and view all the answers

    What is essential to successfully communicate with peripherals using the PPI 8255?

    <p>Steps including writing a control word and I/O instructions</p> Signup and view all the answers

    What is a key advantage of the PPI 8255 regarding its cost?

    <p>It provides extensive functionality at a low cost</p> Signup and view all the answers

    How does the PPI 8255 improve system performance?

    <p>By offloading I/O operations from the CPU</p> Signup and view all the answers

    In which mode does the PPI 8255 lack interrupt handling capabilities?

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

    Which of the following accurately describes the complexity of using the PPI 8255?

    <p>It is complex and may be challenging for novices</p> Signup and view all the answers

    Which applications are commonly associated with the PPI 8255?

    <p>Traffic light control, interfacing with motors, and waveform generation</p> Signup and view all the answers

    What characterizes the versatility of the PPI 8255?

    <p>It supports multiple modes for each of its ports</p> Signup and view all the answers

    What limitation affects the PPI 8255's resolution?

    <p>It has a maximum resolution of 8 bits per port</p> Signup and view all the answers

    Study Notes

    Programmable Peripheral Interface PPI (8255)

    • The 8255 is a general-purpose programmable I/O device used to interface a CPU with external devices like ADCs, DACs, and keyboards.
    • It consists of three 8-bit bidirectional I/O ports: Port A, Port B, and Port C.
    • Each port can be programmed to function as input or output.
    • Port C can be further divided into two 4-bit ports, Port C Lower and Port C Upper.
    • Port C can operate in either BSR (Bit Set Reset) mode or input/output mode.
    • The 8255 has two control groups: Control Group A (Port A and Port C Upper) and Control Group B (Port C Lower and Port B).
    • Different ports can be selected for different modes by writing a control word to the control register based on the values of CS', A1, and A0.
    • The 8255 operates in two modes: BSR mode and input/output mode.

    BSR Mode

    • The 8255 works in BSR mode when the most significant bit (D7) of the control word is 0.
    • Only Port C bits are used to set or reset specific bits.

    Input/Output Mode

    • The 8255 works in input/output mode when D7 is 1.
    • This mode has three sub-modes: Mode 0, Mode 1, and Mode 2.
    Mode 0
    • All three ports (Port A, Port B, and Port C) can be configured as either simple input or simple output.
    • No interrupt handling capabilities are available in this mode.
    Mode 1
    • Either Port A or Port B can be configured as input or output.
    • Port C bits are used as handshake signals for synchronized data transmission.
    • Interrupt handling capabilities are available in this mode.
    Mode 2
    • Only Port A functions as a bi-directional data bus.
    • Port B can be configured in either Mode 0 or Mode 1.
    • 6 bits of Port C are used as handshake signals.
    • Interrupt handling capabilities are available in this mode.

    Programmable Interrupt Controller PIC (8259)

    • The 8259 is a Programmable Interrupt Controller (PIC) used to increase the interrupt-handling capabilities of a microprocessor.
    • It combines multiple interrupt input sources into a single interrupt output.
    • It provides 8 interrupt lines, IR0 to IR7.
    • It can be programmed for either edge-triggered or level-triggered mode.
    • Individual interrupt request register bits can be masked to selectively disable certain interrupt requests.
    • Cascading multiple 8259 chips allows for up to 64 interrupt lines.
    • The 8259 has various blocks: Data bus buffer, R/W Control Logic, Control Logic, Interrupt Request Register, Interrupt Service Register, Interrupt Mask Register, Priority Resolver, and Cascade Buffer.

    Universal Synchronous Asynchronous Receiver Transmitter USART (8251)

    • The 8251 USART (Universal Synchronous Asynchronous Receiver Transmitter) acts as a mediator between a microprocessor and peripherals for serial data transmission.
    • It converts serial data from peripherals into parallel data for the CPU.
    • It also converts parallel data from the CPU into serial data for peripherals.
    • It consists of blocks: Data bus buffer, Read/Write control logic, Modem control, Transmit buffer, Transmit control, Receive buffer, and Receive control.

    Programmable Interval Timer PIT (8253)

    • The 8253 and 8254 are programmable interval timers (PITs) used for timing and counting functions.
    • They have three independent 16-bit down counters, each with two input pins (Clock & Gate) and one output pin (OUT).
    • When a 16-bit count is loaded into a counter, it decrements the count until it reaches 0 and then generates a pulse that can be used to interrupt the CPU.
    • They support both binary and BCD counting modes.
    • They are compatible with various microprocessors.
    • The 8254 includes a Read Back command to check count values, programmed mode, current mode, and counter status.
    • It features a data bus buffer, Read/Write control logic, and a control word register.
    • Each of the three counters has a dedicated control word to configure its operation.

    Programmable Interfacing Devices

    • Programmable interfacing devices are integrated circuits designed to interface a CPU with peripheral devices, facilitating communication and control.
    • They are often programmable, allowing customization for specific applications.

    Programmable Peripheral Interface (PPI) 8255

    • This device is a general-purpose programmable I/O IC designed to interface the CPU with external devices like ADCs, DACs, and keyboards.
    • It has three 8-bit bidirectional I/O ports: Port A, Port B, and Port C, each configurable as input or output.
    • Port C can be divided into two 4-bit ports for specialized functions.

    Operating Modes

    • Bit Set Reset (BSR) Mode: Port C bits are used for setting or resetting individual bits.
    • Input-Output Mode: Ports can be configured for various input/output functions, divided into three modes:
      • Mode 0: All ports work as simple input or output, with no interrupt handling.
      • Mode 1: Handshake I/O, allowing synchronized data transfer with peripherals using handshake signals.
      • Mode 2: Bidirectional data bus, with Port A operating in bidirectional mode and Port B using Mode 0 or Mode 1.

    Programming

    • The 8255 is programmed by writing control words to a control register, determining the operational mode and port configuration.
    • The control word has 8 bits, with the most significant bit (D7) indicating the operating mode (0 for BSR, 1 for I/O).

    Programmable Interrupt Controller (PIC) 8259

    • An IC designed to expand the interrupt handling capabilities of a microprocessor.
    • It combines multiple interrupt sources into a single interrupt output, allowing for more efficient interrupt management.
    • It provides eight interrupt request lines (IR0 to IR7) and can be programmed for edge or level-triggered operation.

    Features

    • Can mask individual interrupt request lines, selectively disabling interruptions.
    • Can be cascaded to increase interrupt handling capacity to 64 interrupt lines.
    • Does not require a clock cycle for operation.

    Universal Synchronous Asynchronous Receiver Transmitter (USART) 8251

    • An IC used to convert serial data to parallel format and vice versa, facilitating communication between the CPU and peripherals.
    • It receives serial data from peripherals and converts it to parallel data for the CPU.
    • It also receives parallel data from the CPU and converts it to serial data for peripherals.
    • It contains various blocks dedicated to data buffering, control logic, and serial-to-parallel/parallel-to-serial conversion.

    Features

    • Can be programmed for both synchronous and asynchronous communication, supported by dedicated modem control pins.
    • Includes error detection capabilities and flow control mechanisms to ensure accurate data transfer.

    Programmable Interval Timer (PIT) 8253/54

    • An IC designed to perform timing and counting functions using three 16-bit down-counters.
    • Each counter has two input pins (CLOCK & GATE) and one output pin (OUT).
    • Counters are programmed to decrement from a loaded count value, generating a pulse upon reaching zero.

    Features

    • Can handle input frequencies up to 10 MHz.
    • Can be programmed for binary or BCD counting.
    • 8254 provides a "Read-Back" command to allow users to examine counter states and settings.

    Architecture

    • It includes three independent counter blocks, a data bus buffer, Read/Write control logic, and a control register.
    • The control register is programmed with a control word to determine the counter operation modes and settings.

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    Description

    Test your knowledge on the 8255 programmable peripheral interface, a crucial device for CPU and external device interaction. This quiz covers its structure, operational modes, and control mechanisms, ensuring a comprehensive understanding of its functionality.

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