Programmable Peripheral Interface (PPI) 8255 Quiz
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Questions and Answers

Which ports of the PPI 8255 can operate in modes 0, 1, or 2 of input-output mode?

  • Port C lower
  • Port C upper
  • Port B
  • Port A (correct)

    • What is the primary function of the control register in the PPI 8255?

  • To configure port settings based on A1, A0 inputs (correct)
  • To manage data transfers between the CPU and I/O
  • To handle interrupts from external devices
  • To set the power supply levels for the device

    • In which mode of the PPI 8255 are only Port C bits utilized to set or reset?

  • Mode 0
  • Bit set reset mode (correct)
  • Input-output mode
  • Mode 1

    • What happens when the MSB of the control word (D7) is set to 1 in the PPI 8255?

    <p>The PPI operates in input-output mode</p> Signup and view all the answers

    What is the voltage requirement for the PPI 8255 operation?

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

    Which of the following ports in PPI 8255 cannot be configured for output functions in mode 0?

    <p>None of the ports</p> Signup and view all the answers

    What signifies that PPI 8255 is in BSR mode based on its control word?

    <p>MSB (D7) is 0</p> Signup and view all the answers

    What differentiates mode 1 from mode 0 in the PPI 8255?

    <p>Mode 1 allows for interrupt handling</p> Signup and view all the answers

    What is a limitation of the 8255 PPI in applications requiring multiple I/O ports?

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

    Which statement correctly describes the function of the Interrupt Request Register (IRR) in the 8259 PIC?

    <p>It stores the interrupt levels requesting service.</p> Signup and view all the answers

    How can the interrupt handling capacity of the 8259 be increased?

    <p>By cascading more 8259 chips.</p> Signup and view all the answers

    What type of data communication does the 8251 USART facilitate?

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

    In the context of the 8259 PIC, what does the Control Logic block primarily manage?

    <p>The flow of read and write operations based on pin states.</p> Signup and view all the answers

    Which feature of the 8251 USART ensures the integrity of data transmitted?

    <p>Parity checking for error detection.</p> Signup and view all the answers

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

    <p>To connect and buffer communication between the 8259 and microprocessors.</p> Signup and view all the answers

    Which mode can the 8259 PIC be programmed in?

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

    What is the principal function of the Receive Control block in the 8251 USART?

    <p>To control the receipt of incoming data.</p> Signup and view all the answers

    What does the Priority Resolver in the 8259 PIC do?

    <p>Activates the highest priority interrupt for servicing.</p> Signup and view all the answers

    What is a characteristic of the 8255 PPI technology?

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

    Which signal indicates that the transmitter of the 8251 USART is ready to transmit data?

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

    What is the function of the Transmit Control block in the 8251 USART?

    <p>To initiate the transmission of data characters.</p> Signup and view all the answers

    What is one disadvantage of the 8251 USART related to data handling?

    <p>It has a limited maximum data transfer rate.</p> Signup and view all the answers

    What technology does the 8254 use in its design?

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

    Which feature allows the user to check the status of a counter in the 8254?

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

    What is a requirement for operating a counter in the 8253 and 8254?

    <p>Loading a 16-bit count in its register</p> Signup and view all the answers

    How many independent counters does the 8254 feature?

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

    What characteristic is NOT true for the 8253?

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

    Which pin is NOT part of the 8254 control signal interface?

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

    What programming mode does the 8253 allow between reads and writes?

    <p>None interleaved reads or writes</p> Signup and view all the answers

    Which element is primarily responsible for interfacing the 8253/54 with the system data bus?

    <p>Data Bus Buffer</p> Signup and view all the answers

    Which mode requires only port C bits for handshake signals prior to data transmission?

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

    What is a significant limitation of the PPI 8255 regarding data transfer speed?

    <p>It is not designed for high-speed data transfer.</p> Signup and view all the answers

    In which mode does only port A function while port B can operate in either Mode 0 or Mode 1?

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

    What characterizes the Bit Set Reset (BSR) mode operation of the PPI 8255?

    <p>It utilizes only port C bits for set and reset operations.</p> Signup and view all the answers

    Which of the following is NOT an application of the PPI 8255?

    <p>High-speed data acquisition</p> Signup and view all the answers

    What is a key benefit of using the PPI 8255 in a microprocessor system?

    <p>It improves system performance by handling I/O operations.</p> Signup and view all the answers

    What is a limitation pertaining to the number of ports in the PPI 8255?

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

    What does a high value of the most significant bit in the control word indicate in the function of the 8255?

    <p>The 8255 will function in Input-Output mode.</p> Signup and view all the answers

    What is a feature of the control register in the PPI 8255?

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

    How many pins does the PPI 8255 have in total?

    <p>40 pins</p> Signup and view all the answers

    Which characteristic is NOT true for the PPI 8255?

    <p>It supports high-speed data transmission.</p> Signup and view all the answers

    Why might the PPI 8255 be considered obsolete?

    <p>Newer I/O interface components offer better functionality.</p> Signup and view all the answers

    Which feature distinguishes Mode 0 from other modes in the PPI 8255?

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

    What does the control word format of the 8255 dictate?

    <p>The operational mode and function of each port.</p> Signup and view all the answers

    Which of the following statements about the PPI 8255's port configuration is true?

    <p>Port C can be divided into two 4-bit ports.</p> Signup and view all the answers

    In which mode is the PPI 8255 unable to handle interrupts?

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

    What is the purpose of the control group B in the PPI 8255 architecture?

    <p>To manage port C lower and port B.</p> Signup and view all the answers

    Which control word scenario results in the PPI 8255 entering BSR mode?

    <p>When D7 is set to 0.</p> Signup and view all the answers

    Which of the following modes allows the PPI 8255 to function with a handshake mechanism?

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

    What is the significance of the input from CS' in PPI 8255's operation?

    <p>It indicates whether the PPI is operational or in a reset state.</p> Signup and view all the answers

    Which characteristic correctly differentiates Mode 1 from BSR mode in the PPI 8255?

    <p>Mode 1 can use all three ports for I/O functions.</p> Signup and view all the answers

    Which function does the control register of the PPI 8255 primarily perform?

    <p>Select and configure ports as input or output.</p> Signup and view all the answers

    What is one of the limitations of the PPI 8255 regarding its data transfer capabilities?

    <p>It is not capable of high-speed data transfer.</p> Signup and view all the answers

    Which mode of the PPI 8255 allows only port A to work while port B operates in either Mode 0 or Mode 1?

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

    What is a significant drawback of the PPI 8255 in terms of resolution?

    <p>It offers only 8 bits of resolution per port.</p> Signup and view all the answers

    What allows the PPI 8255 to operate in various modes, enhancing its versatility?

    <p>Control word programming.</p> Signup and view all the answers

    Which application is NOT typically associated with the PPI 8255?

    <p>Biometric data processing</p> Signup and view all the answers

    What aspect of the PPI 8255 contributes to its cost-effectiveness?

    <p>It is a relatively low-cost component.</p> Signup and view all the answers

    Which characteristic is true for the BSR mode of operation in the PPI 8255?

    <p>It utilizes port C bits for set/reset operations.</p> Signup and view all the answers

    What must be done before communicating with peripherals through the PPI 8255?

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

    What is a common disadvantage of using the PPI 8255 in a microprocessor system?

    <p>It adds complexity for novice programmers.</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 feature relates to the Control Word's purpose in the PPI 8255?

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

    What type of performance improvement does the use of an 8255 PPI provide to a microprocessor system?

    <p>Improves system efficiency by handling I/O operations.</p> Signup and view all the answers

    What is a design characteristic of the PPI 8255 that affects its external connections?

    <p>Two 8-bit parallel ports and one control port.</p> Signup and view all the answers

    What is the primary limitation of the 8255 PPI regarding the number of available I/O ports?

    <p>It can support only 3 8-bit ports.</p> Signup and view all the answers

    Which feature allows the 8259 PIC to handle multiple interrupt sources efficiently?

    <p>Cascading chips to increase interrupt lines.</p> Signup and view all the answers

    What is the primary purpose of the Data Bus Buffer in the 8259 PIC?

    <p>To transfer data between the microprocessor and the PIC.</p> Signup and view all the answers

    How does the 8251 USART manage data transmission?

    <p>Transmits data in both serial and parallel formats during operations.</p> Signup and view all the answers

    What mode can the 8259 Programmable Interrupt Controller be programmed in?

    <p>Edge or level triggered mode.</p> Signup and view all the answers

    What does the Priority Resolver in the 8259 PIC do?

    <p>It sets the priorities of all interrupts by analyzing register levels.</p> Signup and view all the answers

    What is a significant advantage of the 8251 USART compared to other communication devices?

    <p>It supports both synchronous and asynchronous communication.</p> Signup and view all the answers

    What is the function of the Interrupt Request Register (IRR) in the 8259 PIC?

    <p>It registers the interrupts that have not been serviced.</p> Signup and view all the answers

    What type of data does the Receive Control block in the 8251 USART handle?

    <p>Both receiving and processing parallel data.</p> Signup and view all the answers

    Which pin in the 8251 USART indicates that the transmitter is ready to send a data character?

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

    How can the 8259 PIC interrupt capacity be expanded?

    <p>Utilizing additional 8259 chips in a cascading configuration.</p> Signup and view all the answers

    What is the significance of the control signals used in the Read/Write control logic of the 8251 USART?

    <p>To facilitate the reading or writing of data to the appropriate registers.</p> Signup and view all the answers

    What is a common application of the 8259 PIC in microprocessor systems?

    <p>To provide enhanced interrupt handling capabilities.</p> Signup and view all the answers

    What role does the Transmit Buffer play in the 8251 USART?

    <p>It is used to convert parallel data to serial format for transmission.</p> Signup and view all the answers

    What is a potential consequence of the limited buffer size in the 8251 USART?

    <p>Data loss may occur if not read promptly.</p> Signup and view all the answers

    Which of the following describes a key difference between the 8253 and 8254 Programmable Interval Timers?

    <p>8254 allows interleaved reads and writes of the same counter.</p> Signup and view all the answers

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

    <p>It has a maximum data transfer rate of 115.2 kbps.</p> Signup and view all the answers

    Which function does the Data Bus Buffer serve in the 8253/54 architecture?

    <p>It acts as a tri-state, bi-directional interface to the system bus.</p> Signup and view all the answers

    What feature does the Read-Back command in the 8254 enable?

    <p>It checks the value, mode, and status of the counter.</p> Signup and view all the answers

    Which of the following does NOT apply to the architecture of the 8254?

    <p>It relies exclusively on PMOS technology.</p> Signup and view all the answers

    What characteristic is unique to the control word register in the 8253/54?

    <p>It allows for configuration of the counter's operational mode.</p> Signup and view all the answers

    Why may programming the USART be considered complex?

    <p>It requires precise timing and consideration of parameters.</p> Signup and view all the answers

    Which statement is true regarding the functionality of the 8253/54 counters?

    <p>Each counter can be independently programmed for counting functions.</p> Signup and view all the answers

    What is a consequence of the limited functionality of the 8251 USART?

    <p>It lacks advanced error correction features.</p> Signup and view all the answers

    Study Notes

    Programmable Peripheral Interface (PPI) 8255

    • A versatile I/O device that interfaces CPUs to external devices like ADCs, DACs, and keyboards.
    • Contains three 8-bit bidirectional I/O ports: Port A, Port B, and Port C.
    • Ports can be programmed as input or output functions.
    • Consists of 40 pins and operates on a +5V regulated power supply.
    • Port C can function in either BSR (Bit-Set-Reset) mode or as part of input/output modes.
    • Port B can function in either Mode 0 or Mode 1 of input/output modes.
    • Port A can function in Mode 0, Mode 1, or Mode 2 of input/output modes.
    • It features two control groups: Control Group A (Port A and Upper Port C) and Control Group B (Lower Port C and Port B).
    • Ports are selected and configured in different modes using a control register, which is accessed based on the values of CS', A1, and A0 pins.

    Bit-Set-Reset (BSR) Mode

    • Enabled when the most significant bit (D7) of the control word is 0.
    • Only Port C bits are used for setting or resetting individual bits.

    Input/Output Mode

    • Enabled when the most significant bit (D7) of the control word is 1.
    • Divided into three modes:
      • Mode 0: All three ports can work as simple input or output ports. No interrupt handling.
      • Mode 1: Either Port A or Port B works as an input or output port, with Port C bits used for handshake signals. Enables interrupt handling and latched input/output.
      • Mode 2: Only Port A works. Port B can operate in Mode 0 or Mode 1. 6 bits of Port C function as handshake signals. Enables interrupt handling.

    Advantages of PPI 8255

    • Versatile: Supports multiple modes of operation for flexible I/O configurations.
    • Easy to use: Simple programming through the control register.
    • Compatible: Widely used, compatible with a wide range of devices and software.
    • Low cost: Affordable option for numerous applications.

    Disadvantages of PPI 8255

    • Limited functionality: Lower data transfer speeds and limited memory capacity compared to newer I/O interfaces.
    • Limited number of ports: Only three 8-bit ports may be insufficient for some applications.
    • Limited resolution: 8-bit resolution per port might not be sufficient for high-resolution applications.
    • Obsolete technology: Being replaced by more advanced I/O interface components.

    Programmable Interrupt Controller (PIC) 8259

    • A microprocessor used to manage interrupts.
    • Enables multiple interrupt sources to be combined into a single interrupt output.
    • Provides 8 individual interrupt lines (IR0 to IR7).
    • Designed for use with 8085 and 8086 microprocessors.
    • Can be programmed in edge-triggered or level-triggered mode.
    • Allows masking of individual interrupt request register bits.
    • Can be cascaded to increase interrupt lines up to 64.
    • Doesn't require clock cycles for operation.
    • Features a 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

    • A device that interfaces a microprocessor with peripherals for serial data transmission and reception.
    • Converts serial data from peripherals into parallel data for the CPU.
    • Converts parallel data from the CPU into serial data for peripherals.
    • Contains blocks for data bus buffer, read/write control logic, modem control, transmit buffer, transmit control, receive buffer, and receive control.

    Advantages of USART 8251

    • Versatility: Supports both synchronous and asynchronous communication modes.
    • Error detection: Features built-in error detection mechanisms like parity checking.
    • Flow control: Enables regulation of data transmission and reception to prevent data loss.
    • Compatibility: Compatible with a wide range of microprocessors.
    • Ease of use: Simple interface pins and registers for programming.

    Disadvantages of USART 8251

    • Limited speed: Relatively low maximum data transfer rate of 115.2 kbps.
    • Limited buffer size: Small internal buffers can result in data loss if data isn't read promptly.
    • Complex programming: Programming requires careful attention to timing and other parameters.
    • Cost: Adds cost to systems, especially when multiple USARTs are needed.
    • Limited functionality: Lacks advanced features like DMA or error correction.

    Programmable Interval Timer (PIT) 8253/8254

    • A device that provides timing and counting functions using three 16-bit registers.
    • Each counter has two inputs (Clock & Gate) and one output (OUT).
    • To operate a counter, a 16-bit count is loaded into its register.
    • Counters decrement the count until reaching 0, then generate a pulse that can interrupt the CPU.

    Differences between 8253 and 8254

    • 8253:
      • Operating frequency: 0-2.6 MHz.
      • Technology: N-MOS.
      • Read-back command: Not available.
      • Interleaving reads/writes: Not allowed for the same counter.
    • 8254:
      • Operating frequency: 0-10 MHz.
      • Technology: H-MOS.
      • Read-back command: Available.
      • Interleaving reads/writes: Allowed for the same counter.

    Features of 8253/8254

    • Three independent 16-bit down counters.
    • Input handling range: DC to 10 MHz.
    • Programmable for binary or BCD counting.
    • Compatible with various microprocessors.
    • 8254 features a READ BACK command to check count value, programmed mode, current mode, and counter status.

    Architecture of 8254

    • Contains three counters, a data bus buffer, read/write control logic, and a control register.
    • Each counter has CLOCK & GATE inputs and an OUT output.

    Pin Description of 8254

    • Data bus buffer: 8-bit, tri-state, bidirectional buffer for communication with the system data bus.
      • Programming counter modes.
      • Loading count registers.
      • Reading count values.
    • Read/Write logic: Controls read/write operations using signals RD, WR, CS, and address lines A0 & A1.
    • Address lines A0 & A1: Select counters or the control word register based on their values.
    • Control word register: Used to program counter modes, read or write operations.
    • CS: Chip select signal.
    • RD: Read signal.
    • WR: Write signal.
    • A0, A1: Address lines.
    • CLK0, CLK1, CLK2: Clock inputs for counters 0, 1, and 2 respectively.
    • GATE0, GATE1, GATE2: Gate inputs for counters 0, 1, and 2 respectively.
    • OUT0, OUT1, OUT2: Output signals for counters 0, 1, and 2 respectively.

    Programmable Peripheral Interface 8255 (PPI)

    • The PPI 8255 is a general purpose programmable I/O device that interfaces a 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.
    • Ports can be configured as input or output functions.
    • Port C is further divided into two 4-bit ports: Port C Lower and Port C Upper.
    • It has two control groups: Control Group A (Port A and Port C Upper) and Control Group B (Port C Lower and Port B).
    • Different modes of operation are selected based on the values of CS', A1, and A0, which are programmed by writing a suitable word in the control register (control word D0-D7).
    • The PPI operates in two main modes: Bit Set/Reset (BSR) mode and Input/Output (I/O) mode.
    • In BSR mode, only Port C bits are used for setting or resetting.
    • In I/O mode, the PPI can be further divided into three modes:
      • Mode 0: All three ports can function as simple input or output ports without interrupt handling capabilities.
      • Mode 1: Either Port A or Port B can function as input or output, while Port C bits are used for handshake signals for data transmission. This mode supports interrupts.
      • Mode 2: Port A operates bi-directionally, while Port B can be in Mode 0 or Mode 1, and 6 bits of Port C function as handshake signals. This mode also supports interrupts.
    • Advantages:
      • Versatility: Supports different modes of operation, making it adaptable to various systems.
      • Ease of use: Simple to program and interface with other devices.
      • Compatibility: Wide compatibility with a variety of devices and software.
      • Low cost: Affordable option for many applications.
    • Disadvantages:
      • Limited functionality: Compared to newer I/O interfaces, it has less functionality. It is not capable of high-speed data transfer and has limited memory capacity.
      • Limited number of ports: Only provides three 8-bit ports, insufficient for some applications.
      • Limited resolution: Provides 8 bits of resolution per port, which might not be enough for high-resolution requirements.
      • Obsolete technology: Being replaced by newer, more advanced I/O interface components.

    Programmable Interrupt Controller (PIC) 8259

    • 8259 is the Programmable Interrupt Controller used with microprocessors like 8085 and 8086.
    • It allows expanding interrupt handling capabilities by combining multiple interrupt sources into a single interrupt output.
    • It provides 8 interrupts, from IR0 to IR7.
    • Features:
      • Programmable in edge-triggered or level-triggered mode.
      • Individual interrupt request register bits can be masked.
      • Can be cascaded to extend interrupt lines up to 64.
      • Does not require a clock cycle.
    • Contains the following blocks:
      • Data Bus Buffer: Communicates with 8085/8086 by acting as a buffer.
      • R/W Control Logic: Controls data flow based on RD and WR signals.
      • Control Logic: Controls functionality of the chip. Features a pin called INTR that takes interrupt requests from microprocessors.
      • Interrupt Request Register (IRR): Stores all interrupt requests.
      • Interrupt Service Register (ISR): Stores the currently serviced interrupt level.
      • Interrupt Mask Register (IMR): Stores interrupt levels that are to be masked.
      • Priority Resolver: Determines the priority of interrupts and sets the highest priority interrupt in ISR, resetting already serviced interrupts in IRR.
      • Cascade Buffer: Allows cascading multiple 8259 chips to increase interrupt capabilities.

    ### Universal Synchronous Asynchronous Receiver Transmitter (USART) 8251

    • 8251 is a USART that acts as an interface between a microprocessor and peripheral devices to transmit serial data into parallel form and vice versa.

    • It receives serial data from peripherals and converts it into parallel data for the CPU.

    • Similarly, it receives parallel data from the CPU and converts it into serial data for peripherals.

    • Contains the following blocks:

      • Data Bus Buffer: Interfaces 8251's internal data bus to the system data bus.
      • Read/Write Control Logic: Controls overall operation by selecting data buffer register, control register, or status register based on input signals.
      • Modem Control: Handles communication over telephone lines or cable using modulator/demodulator (modem). Includes DSR (Data Set Ready), DTR (Data Terminal Ready), CTS (Clear To Send), and RTS (Request To Send) signals.
      • Transmit Buffer: Converts a parallel byte into a serial signal and transmits it to the common channel. Includes a TXD (Transmit Data) signal.
      • Transmit Control: Controls data transmission. Includes signals like TXRDY (Transmitter Ready), TXEMPTY (Transmitter Empty), and TXC (Transmit Clock).
      • Receive Buffer: Acts as a buffer for received data. Includes an RXD (Receive Data) signal.
      • Receive Control: Controls data reception. Includes signals like RXRDY (Receiver Ready) and RXC (Receive Clock).
      • SYNDET/BD: Used for external synchronous mode (input) and asynchronous mode (output).

    • Advantages of USART:

      • Versatility: Supports both synchronous & asynchronous communication.
      • Error detection: Features parity checking for data accuracy.
      • Flow control: Regulates data transmission & reception, preventing data loss.
      • Compatibility: Widely compatible with various microprocessors.
      • Ease of use: Simple interface pins and registers make programming relatively easy.

    • Disadvantages of USART:

      • Limited speed: Maximum data transfer rate is relatively low.
      • Limited buffer size: Small internal buffer can cause data loss if data is not read promptly.
      • Complex programming: Programming requires careful attention to timing and other parameters.
      • Cost: Adds cost to a system, especially if multiple USARTs are needed
      • Limited Functionality: Does not include more advanced features like DMA or advanced error correction.

    Programmable Interval Timer (PIT) 8253 and 8254

    • Intel 8253 and 8254 are programmable interval timers (PITs) that perform timing and counting functions using three 16-bit registers.

    • Each counter has two input pins: Clock and Gate, and an output pin: OUT.

    • To operate a counter, a 16-bit count is loaded into its register.

    • When commanded, it decrements the count to zero, generating a pulse that can interrupt the CPU.

    • Differences between 8253 and 8254:

      • 8253 frequency: 0-2.6 MHz
      • 8254 frequency: 0-10 MHz
      • 8253 technology: N-MOS
      • 8254 technology: H-MOS
      • 8253: No Read-Back command
      • 8254: Features a Read-Back command
      • 8253: Read/Write of the same counter cannot be interleaved.
      • 8254: Read/Write of the same counter can be interleaved.

    • Features of 8253/54:

      • Three independent 16-bit down counters.
      • Input handling from DC to 10 MHz.
      • Programmable for binary or BCD count.
      • Compatible with most microprocessors.
      • 8254 has a Read-Back command to check counter’s count value, programmed mode, current mode, and status.

    • 8254 Architecture: Includes three counters, a data bus buffer, Read/Write control logic, and a control register.

    • 8254 Pin Description: Clock, Gate, OUT, CS, A1, A0, RD, WR, D0-D7, RESET.

    • Data Bus Buffer:

      • Tri-state, bi-directional, 8-bit buffer that interfaces 8253/54 to the system data bus.
      • Functions: Programming 8253/54 modes, loading count registers, and reading count values.

    • Read/Write Logic:

      • Contains signals RD, WR, CS, A0, and A1.
      • Connected to IOR and IOW (peripheral mode) or MEMR and MEMW (memory-mapped mode) depending on configuration.
      • A0 and A1 lines select the control word register or the counters based on their logic levels.

    • Control Word Register:

      • Accessed with A0 and A1 at logic 1.
      • Used to write a command word that specifies the counter, mode, and the operation (read or write).

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    Test your knowledge about the PPI 8255, a versatile I/O device that connects CPUs to external devices. This quiz covers its ports, modes of operation, and control features. Find out how well you understand the functionality and applications of this important programmable device.

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