Minimum Mode 8086 System and Timings

Minimum Mode 8086 System and Timings

In a minimum mode 8086 system, the microprocessor 8086 is operated in minimum mode by connecting its MN/MX pin to logic 1. 

In this mode, all the control signals are given out by the microprocessor chip itself.

There is a single microprocessor in the single mode system.

The remaining components in the system are latches, trans receivers, clock generator, memory and I/O devices, chip selection logic for selecting memory or I/O devices. à The latches are generally buffered output D-type flip-flops like 74LS373.

They are used for separating the valid address from the multiplexed address/data signals and are controlled by the ALE signal generated by 8086.

Trans receivers are the bi-directional buffers and are sometimes called data amplifiers.

They are required to separate the valid data from the time multiplexed address/data signals.

They are controlled by two signals namely DEN and DT/R.

The DEN signal indicates the valid data available on the data bus while DT/R indicates the direction of data, i.e., from / to the processor.

The system contains memory (RAM or ROM), I/O devices for the communication with the processor.

The clock generator (IC8284) generates the clock from the crystal oscillator and is used as an accurate timing reference for the system.

The clock generator also synchronizes some external signals with the system clock.

Since it has 20 address lines and 16 data lines, the 8086 CPU requires three octal address latches and two octal data buffers for the complete address and data separation.

The working of the minimum mode configuration system can be better described in terms of the timing diagrams.

The timing diagram can be categorized into two parts. The first is the timing diagram for read cycle and second is the write cycle.

The read cycle begins in T₁ with the assertion of the Address Latch Enable(ALE) signal and M/IO signal.