Even the hardware of these microprocessors is similar to the earlier versions. This chapter presents an overview of each microprocessor and points out the differences or enhancements that are present in each version. Intel has added four new versions of each of these embedded controllers to its lineup of microprocessors. Detail the differences between the various versions of the and embedded controllers. Develop software using the enhancements provided in these microprocessors.
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Even the hardware of these microprocessors is similar to the earlier versions. This chapter presents an overview of each microprocessor and points out the differences or enhancements that are present in each version. Intel has added four new versions of each of these embedded controllers to its lineup of microprocessors.
Detail the differences between the various versions of the and embedded controllers. Develop software using the enhancements provided in these microprocessors. Describe the operation of the memory management unit MMU within the microprocessor. Define and detail the operation of a real-time operating system RTOS. The only difference between the and is the width of their data buses.
The like the contains a bit data bus, while the like the contains an 8-bit data bus. The and are often called embedded controllers because of their applica- tion as a controller, not as a microprocessor-based computer. Table 16—1 lists each version and the major features provided. Notice that this microprocessor has a great deal more internal circuitry than the The block diagrams of the and are identical except for the prefetch queue, which is four bytes in the and six bytes in the More details on the operation of each enhancement and details of each advanced version are provided later in the chapter.
Clock Generator. This reduces the component count in a system. The CLKOUT pin drives other devices in a system and provides a timing source to additional microprocessors in the system. Programmable Interrupt Controller. Note that the number of available interrupts depends on the version: The EB version has six interrupt inputs and the EC version has In many systems, the five interrupt inputs are adequate. The timer section contains three fully programmable l6-bit timers.
They are also used to count external events. The third timer, timer 2, is internal and clocked by the master clock. The output of timer 2 generates an interrupt after a specified number of clocks and can provide a clock to the other timers. Timer 2 can also be used as a watchdog timer because it can be programmed to interrupt the microprocessor after a certain length of time. The watchdog timer is a bit counter that is clocked internally by the CLKOUT signal one half the crystal frequency.
This output can be used for any purpose: It can be wired to the reset input to cause a reset or to the NMI input to cause an interrupt.
Note that if it is connected to the reset or NMI inputs, it is periodically reprogrammed so that it never counts down to zero. The purpose of a watchdog timer is to reset or interrupt the system if the software goes awry.
Programmable DMA Unit. Programmable Chip Selection Unit. The lower memory select signal enables memory for the interrupt vectors, the upper memory select signal enables memory for reset, and the middle memory select signals enable up to four middle memory devices. The sizes of the memory areas are programmable, and wait states 0—3 waits can be automatically inserted with the selection of an area of memory. The power save feature allows the system clock to be divided by 4, 8, or 16 to reduce power consumption.
The power-saving feature is started by soft- ware and exited by a hardware event such as an interrupt. The power down feature stops the clock completely, but it is not available on the XL version.
The power down mode is entered by execution of an HLT instruction and is exited by any interrupt. Refresh Control Unit. The refresh control unit generates the refresh row address at the interval programmed. The refresh control unit does not multiplex the address for the DRAM—this is still the responsibility of the system designer. The refresh address is provided to the memory system at the end of the programmed refresh interval, along with the RFSH control signal.
The memory system must run a refresh cycle during the active time of the RFSH control signal. More on memory and refreshing is provided in the section that explains the chip selection unit. Pin Definitions. The enhanced versions are described later in this chapter. VSS This is the system ground connection. X1 and X2 The clock pins are generally connected to a fundamental-mode parallel resonant crystal that operates an internal crystal oscillator.
An external clock signal may be connected to the X1 pin. The internal master clock operates at one half the external crystal or clock input signal. For a proper reset, the RES must be held low for at least 50 ms after power is applied. This pin is often connected to an RC circuit that generates a reset signal after power is applied. Tin0 and Tin1 These pins are used as external clocking sources to timers 0 and 1.
Tout0 and Tout1 These pins provide the output signals from timers 0 and 1, which can be programmed to provide square waves or pulses. NMI This is a non-maskable interrupt input. It is positive edge-triggered and always active. When NMI is activated, it uses interrupt vector 2. Status bits found on address pins A18—A16 have no system function and are used during manufacturing for testing.
If ONCE is held low on a reset, the microprocessor enters a testing mode. BHE The bus high enable pin indicates when a logic 0 that valid data are transferred through data bus connections D15—D8. Even though the status bits on A19—A16 are not used in the system, they must still be demultiplexed. S2, S1, and S0 These are status bits that provide the system with the type of bus transfer in effect. See Table 16—2 for the states of the status bits.
The upper-memory chip select pin selects memory on the upper portion of the memory map. The lower-memory chip select pin enables memory beginning at location H. This pin is programmed to select memory sizes from 1K to K bytes. The middle-memory chip select pins enable four middle memory devices.
These pins are programmable to select an 8K to K byte block of memory, containing four devices. Note that these pins are not present on the EB and EC versions. These are five different peripheral selection lines. Note that the lines are not present on the EB and EC versions. These lines are not present on the EB and EC versions. The data bus enable pin enables the external data bus buffers. DC Operating Characteristics It is necessary to know the DC operating characteristics before attempting to interface or operate the microprocessor.
Each output pin provides 3. A bus cycle for the 8 MHz version requires ns, while the 16 MHz version requires ns. Memory Access Time. A close examination of the timing diagram reveals that the address appears on the address bus TCLAV time after the start of T1. See Figure 16—5.
Access time for the 8 MHz microprocessor is ns - 44 ns - 20 ns, or ns.
Execution Unit Memory Management Unit As we have already discussed that the possess the ability of 3 stage pipelining thus performs fetching, decoding and execution simultaneously along with memory management and bus accessing. Thus all these units operate parallely. This pipelining technique leads to reduction in overall processing time thereby increasing the performance of the overall system. Let us now move further and understand the operation of each unit in detail.
Description[ edit ] Features and performance[ edit ] The series was generally intended for embedded systems , as microcontrollers with external memory. Therefore, to reduce the number of integrated circuits required, it included features such as clock generator , interrupt controller , timers , wait state generator, DMA channels, and external chip select lines. Multiply and divide also showed great improvement being several times as fast as on the original and multi-bit shifts were done almost four times as quickly as in the A useful immediate mode was added for the push, imul, and multi-bit shift instructions.
Microprocessor - 8086 Overview