Typical Microprocessor Based System
• 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
8086/8088 Detailed Memory Interface
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
• Maximum mode is designed to be used with a coprocessor exists in
• All the control signals (except RD ) are not generated by the
• But we still need those control signals.