Signal descriptions of 8086

Signal descriptions of 8086

Modes of operations 

• Minimum mode 

• Maximum mode

In order to implement many situations in a microcomputer system, 8086 has been designed to work in two operating modes:
1.Minimum mode
         -used for small systems with a single processor
2.Maximum mode

         -used for medium to large systems, which often include two or more processors


     

Pin diagram

3 groups of signals:
    -signals with common functions in min and max mode
    -signals with special functions in min mode
    -signals with special functions in max mode

Signals with common functions in min and max mode:

1.AD15-AD0

2.A19/S6-A16/S3
  ___
3.BHE/S7
4.NMI
5.INTR
6.CLK
7.RESET

Signals with common functions in min and max mode:

8.READY 

 _____

9.TEST
    ___
10.RD
            __
11.MN/MX

AD15-AD0

Acts as the address during the first part of the machine cycle and data bus for the remaining part of the machine cycle

A19/S6-A16/S3

• Time multiplexed address/status lines

• During the first part of the machine cycle,these lines are the most significant address lines for memory operations

• During I/O operations, these lines are low.

• During memory or I/O operations, status information is available on these lines during the reamining part of the machine cycle
  
  

• S4 and S3 combinedly indicate which register segment is presently being used for memory access

address and status lines

* Status line S6 is always low
* The address bits are separated from the status bits using latches controlled by the ALE signal.

Bus high enable/S7

* used to indicate the transfer of data over the higher order data bus

* goes low for the data transfers over D15-D8 and is used to derive chip selects of odd address memory bank or peripherals.

* if high,the transfer is made on lower order byte D7-D0