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1、Chapter 9 and Chapter 11 8088, 80286 Microprocessors and ISA Bus I/O and The 8255; ISA Bus Interfacing,Main Contents,State the function of the pins of the 8088 List the functions of the 8088 data, address, and control busesState the differences in the 8088 microprocessor in maximum modeversus minimu
2、m modes Explain how bus arbitration between the CPU and DMA is accomplished,State the function of I/O ports Read and write data to and from I/O portsDesign of peripheral I/O using the 74LS373 output latch and the74LS244 input buffer I/O address map of 80x86 PCsThe purpose of the 8255 chipCode Assemb
3、ly language instructions to perform I/O through the 8255,Main Contents,Sec.9.1 8088 Microprocessor,8088 Microprocessor,The first IBM PC used the 8088 microprocessor, and modern PCs still carry that legacy. The 8088 is internally identical to the 8086, but has only an 8-bit external data bus. The 808
4、8 is a 40-pin microprocessor that can work in two modes: minimum mode and maximum mode. Maximum mode is used when we need to connect the 8088 to an 8087 math coprocessor.,Sec.9.1 8088 Microprocessor,Data bus in 8088,Sec.9.1 8088 Microprocessor,Data bus in 8088,8088 has 8-bit external data bus, pins
5、916 (AD0AD7) are used for both data and addresses. At the time of design of this microprocessor in the late 1970s, due to IC chip packaging limitations, there was a great effort to use the minimum number of pins for external connections.,Sec.9.1 8088 Microprocessor,Data bus in 8088,The ALE pin signa
6、ls whether the information on pins AD0AD7 is address or data. When ALE=1, it indicate that the information on the pins AD0AD7 is the address (A0A7). When ALE=0, it indicate that the information on the pins AD0AD7 is the data (D0D7).,Sec.9.1 8088 Microprocessor,Address bus in 8088,The 8088 has 20 add
7、ress pins (A0A19) allowing it to address a maximum of one megabyte of memory (1M). Pins AD0AD7 provide the A0A7 addresses with the assistance of a latch. To demultiplex the address signals from the address/data pins, a latch must be used tograb the addresses.,Sec.9.1 8088 Microprocessor,Address bus
8、in 8088,Sec.9.1 8088 Microprocessor,Address bus in 8088,A19/S6A16/S3 The address/data bus bits are multiplexed to provide address signals A19-A16 and also status bits S6-S3. Status bit S6 is always a logic 0, bit S5 indicates the condition of IF flag bit, and S4 and S3 show which segment is accessed
9、 during the current bus cycle.,Sec.9.1 8088 Microprocessor,Address bus in 8088,Sec.9.1 8088 Microprocessor,8088 Control bus (Reading and writing),The 8088 can access both memory and I/O devices for read and write operations. This gives us four operations for which we need four control signals: MEMR
10、(memory read), MEMW (memory write), IOR (I/O read), and IOW (I/O write). The four control signals are relativeto three pins ( ).,Sec.9.1 8088 Microprocessor,8088 Control bus,Sec.9.1 8088 Microprocessor,8088 Control bus,Sec.9.1 8088 Microprocessor,Bus timing of 8088,The clock frequency is 5MHz in 808
11、8, so the period of clock cycle is 200ns.In IBM PC, the clock frequency is 4.77MHz, so the period of clock cycle is 210ns. The basic bus cycle in 8088 includes 4 clock cycles.,Sec.9.1 8088 Microprocessor,Bus timing of 8088,In Figure 9-6 the timing for ALE is shown. The 8088 uses 4 clocks for memory
12、and I/O bus activities.,Sec.9.1 8088 Microprocessor,Other 8088 pins,Pins 24-32 of the 8088 have different functions depending on whether the 8088 is used in minimum mode or maximum mode. As stated earlier, maximum mode is used only when we want to connect the 8088 to an 8087 math coprocessor. Table
13、9-2 lists the functions of pins 24-32 of the 8088 in minimum mode.,Sec.9.1 8088 Microprocessor,Other 8088 pins,INTA: interrupt acknowledge, Active-low output signal. ALE: address latch enable, Active-high output signal.DEN: data enable, Active-low output signal.DT/R: data transmit / receive, output
14、signal. Active-low indicates CPU receives data, Active-high indicates CPU sends data.IO/M: input-output or memory, indicates whether address bus is accessing memory or IO device.WR: write, Active-low, output signalRD: read, Active-low, output signalHOLD: Active-high input signal from DMA.HLDA: hold
15、acknowledge, Active-high output signal.,Sec.9.1 8088 Microprocessor,Other 8088 pins,MN/MX: minimum / maximum, Active-low indicate maximum mode. NMI: nonmaskable interrupt, this is a edge-triggered (going from low to high) input signal. INTR: interrupt request, Active-high input signal. CLOCK: Clock
16、is an input signal and is connected to 8284 clock generator. Ready: is an input signal used to insert a wait state for slower memories and I/O. TEST: In maximum mode, is an input from the 8087. RESET: to terminate the present activities of the microprocessor, Active-high, input signal SS0: is equivalent to the S0 pin in maximum mode.,Sec.9.1 8088 Microprocessor,IP and Segment register Contents after Reset,Sec.11.1 8088 Input/Output instructions,
