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Designing the 8086/8088 Microcomputer System

Designing the 8086/8088 Microcomputer System. Typical Microprocessor Based System. Control. Memory/IO. CPU. Address. Data. 8086/8088 Busses. Address Bus 20 address lines so a 2 20 byte address space. Pins A0-A19 provide the address

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Designing the 8086/8088 Microcomputer System

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  1. Designing the 8086/8088 Microcomputer System

  2. Typical Microprocessor Based System Control Memory/IO CPU Address Data

  3. 8086/8088 Busses • Address Bus • 20 address lines so a 220 byte address space. • Pins A0-A19 provide the address • For 8086, A0-A15 are multiplexed with D0-D15 to form AD0-AD15 • For 8088, A0-A7 are multiplexed with D0-D7 to form AD0-AD7 • Data Bus • For 8086, 16 bit data bus D0-D15 (multiplexed as AD0-AD15) • For 8088, 8 bit data bus D0-D7 (multiplexed as AD0-AD7) • Control Bus • For memory access, the following pins are used: RD’, WR’, M/IO’, DT/R’, DEN’, ALE, BHE’ • Other input signals to control 8086 performance: clk ,reset , ready , hold , test’, intr , nmi ,mn’/mx - The intr and hold are acknowledged through intra and holda respectively.

  4. 8086/8088 Pin Configuration

  5. 8086 Control Pins

  6. 8284A

  7. Clock Generator

  8. Ready logic (adding wait states)

  9. 8086/8088 Detailed Memory Interface CS’,WE’,OE’ Control Control MEMORY Address Decoding Unique per device Latches Buffers Demultiplexing 8086/8 Partial Address Address Multiplexed Addr/Data Data

  10. 8088 Bus Structure

  11. 8086 maximum & minimum modes • The mode is controlled by MN/MX. • Maximum mode is obtained by connecting MN/MX to high and minimum mode is by connecting it to high. • Having two different modes (minimum and maximum) is used only 8088/8086. • Each mode enables a different control structure. • Minimum mode operation and control signals are very similar to those of 8085. • So 8085 8-bit peripherals can be used with 8086 without special considerations. • Easy and least expensive way to build single processor systems

  12. 8086/8088 Pin Configuration Differences

  13. Maximum mode • Maximum mode is designed to be used with a coprocessor exists in the system. • All the control signals (except RD ) are not generated by the microprocessor. • But we still need those control signals. • Solution: • 8288.

  14. S2 S1 S0 operationsignal 0 0 0 Interrupt Acknowledge INTA 0 0 1 Read I/O port IORC 0 1 0 Write I/O port IOWC, AIOWC 0 1 1 Halt none 1 0 0 Instruction Fetch MRDC 1 0 1 Read Memory MRDC 1 1 0 Write Memory MWTC, AMWC 1 1 1 Passive none

  15. QS1 QS0 0 0 No instruction taken from queue. 0 1 First byte of current instruction taken from queue. 1 0 Queue flushed. 1 1 Byte other than first byte taken from queue.

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