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Difference Between Minimum Mode and Maximum Mode in 8086 Microprocessor

Last Updated : 25 Apr, 2023
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Introduction :

In the 8086 microprocessor, there are two modes of operation: minimum mode and maximum mode.

Minimum mode is used when the 8086 microprocessor is operating as a standalone processor without any external coprocessors or support chips. In this mode, the 8086 uses a single 8-bit bus for both data and instructions, and a single 20-bit address bus. The minimum mode requires a minimum set of support chips, such as clock generator, address latch, and bus controller.

Maximum mode is used when the 8086 microprocessor is operating with one or more external coprocessors or support chips. In this mode, the 8086 uses a multiplexed bus for data and instructions, and a 20-bit address bus. The maximum mode requires additional support chips, such as a bus controller, a clock generator, and a data buffer.

An 8086 is a 16-bit HMOS microprocessor. It is available in 40 pin DIP chip. It uses a 5V DC supply for its operation. The 8086 uses a 20-line address bus. It has a 16-line data bus. The 20 lines of the address bus operate in multiplexed mode. The 16-low order address bus lines have been multiplexed with data and 4 high-order address bus lines have been multiplexed with status signals. 

Minimum Mode

When MN/MX' = 1, the 8086 microprocessor runs in the minimum mode. All the control signals required for memory operations and I/O interfaces are provided by the system's only processor running in minimum mode, the 8086, alone. The circuit in this case is simple, but it does not permit multiprocessing.

In this mode, the microprocessor chip itself transmits all control signals. The system's latches, transceiver, clock generator, memory, and I/O devices make up the remaining parts.

Minimum mode in 8086
 

Maximum Mode

When 8086 is used as more than just a processor to perform calculations, that is when 8086 is operating in maximum mode. The MN/MX pin is connected to the ground to operate the 8086 in maximum mode. The system's components are identical to those in the minimum mode system.

 

Difference between minimum mode and maximum mode in 8086 microprocessor

Minimum mode Maximum mode 
There can be only one processor.There can be multiple processors.
Performance is slower.Performance is faster.
The circuit is simple.The circuit is complex.
Multiprocessing cannot be performed.Multiprocessing can be performed.
MN/MX is 1 to indicate the minimum mode.MN/MX is 0 to indicate the maximum mode 
The 8086 generates INTA for interrupt acknowledgment.The 8288 Bus Controller generates the interrupt acknowledgment signal (INTA).
The 8086 itself provides an ALE for the latch.Because there are several processors, the 8288 bus controller provides ALE for the latch.
The system is more affordable.The system costs more money.
It is used for small systems.It is used for large systems. 
The multiprocessor setup is not supported.The multiprocessor configuration is accepted.
FeatureMinimum Mode Maximum Mode
Bus width8-bit Multiplexed bus
 
Address bus width 20-bit 20-bit
 
Control signal Single bus control signal Multiple bus control signals
 
Additional support chips Fewer support chips required Additional support chips required
 
Coprocessor support Not supported Supported
 
Maximum number of coprocessors 0 Up to 3
 
Bus controller Not required Required
 
Clock generator Required
 		Required
 
Data buffer Not required Required
 
Interrupt controller  Built-inExternal
 
Interrupt controller Not available Available
 

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