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DIRECT MEMORY ACCESS AND DMA-CONTROLLED I/O INTRODUCTION In previous chapters, we discussed basic and interrupt-processed I/O. Now we turn to the final form of I/O called direct memory access (DMA). The DMA I/O technique provides direct access to the memory while the microprocessor is temporarily disabled. This allows data to be transferred between memory and […]
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QUESTIONS AND PROBLEMS 1. What is interrupted by an interrupt? 2. Define the term interrupt. 3. What is called by an interrupt? 4. Why do interrupts free up time for the microprocessor? 5. List the interrupt pins found on the microprocessor. 6. List the five interrupt instructions for the microprocessor. 7. What is an interrupt […]
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INTERRUPT EXAMPLES This section of the text presents a real-time clock and an interrupt-processed keyboard as examples of interrupt applications. A real-time (RTC) clock keeps time in real time—that is, in hours and minutes. It is also used for precision time delays. The example illustrated here keeps time in Modem Control Register Modem Status Register […]
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SUMMARY 1. An interrupt is a hardware- or software-initiated call that interrupts the currently executing program at any point and calls a procedure. The procedure is called by the interrupt handler or an interrupt service procedure. 2. Interrupts are useful when an I/O device needs to be serviced only occasionally at low data transfer rates. […]
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HARDWARE INTERRUPTS The microprocessor has two hardware interrupt inputs: nonmaskable interrupt (NMI) and interrupt request (INTR). Whenever the NMI input is activated, a type 2 interrupt occurs because NMI is internally decoded. The INTR input must be externally decoded to select a vector. Any interrupt vector can be chosen for the INTR pin, but we […]
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8259A PROGRAMMABLE INTERRUPT CONTROLLER The 8259A programmable interrupt controller (PIC) adds eight vectored priority encoded interrupts to the microprocessor. This controller can be expanded, without additional hardware, to accept up to 64 interrupt requests. This expansion requires a master 8259A and eight 8259A slaves. A pair of these controllers still resides and is programmed as […]
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EXPANDING THE INTERRUPT STRUCTURE This text covers three of the more common methods of expanding the interrupt structure of the microprocessor. In this section, we explain how, with software and some hardware modification of the circuit shown in Figure 12–10, it is possible to expand the INTR input so that it accepts seven interrupt inputs. […]
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INTERRUPTS INTRODUCTION In this chapter, the coverage of basic I/O and programmable peripheral interfaces is expanded by examining a technique called interrupt-processed I/O. An interrupt is a hardware-initiated procedure that interrupts whatever program is currently executing. This chapter provides examples and a detailed explanation of the interrupt structure of the entire Intel family of microprocessors. […]
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QUESTIONS AND PROBLEMS 1. Explain which way the data flow for an IN and an OUT instruction. 2. Where is the I/O port number stored for a fixed I/O instruction? 3. Where is the I/O port number stored for a variable I/O instruction? 4. Where is the I/O port number stored for a string I/O […]
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SUMMARY 1. The 8086–Core2 microprocessors have two basic types of I/O instructions: IN and OUT. The IN instruction inputs data from an external I/O device into either the AL (8-bit) or AX (16-bit) register. The IN instruction is available as a fixed port instruction, a variable port instruction, or a string instruction (80286–Pentium 4) INSB […]
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