ALE signal of 8086/8088

Many students and teachers also confused with the meaning of the signal ALE of some microprocessors. Here, I am explaining it.

The meaning of ALE is address latch enable. This is a special pin of 8086/8088 processor. 8086 is one of the microprocessor which has multiplexed address/data lines i.e. same 16 lines are used for both address and data transfer operations (named AD0 to AD15). As these lines are multiplexed, at a time either address or data will be allowed to transfer through it. In general computer architecture, for any kind of operation (R/W), the address for the operation is generated first and then data transfer operation is performed. Means, at a time both of these operations are not performed. When processor transfers address on AD0-AD15, it makes ALE pin high to suggest the multiplexed lines contain address on it. When this pin becomes low, data is transferred after inserting some propagation delay between operations. That means, same lines will be used for multiple operations. Observe the timing diagram of this operation here. 

Timing Diagram of ALE

The latch is used to separate the address and data lines from AD0 to AD15 as shown in the below figure, ALE signal is connected to the strobe line of the latch.

Working of ALE with Latch

For more information, refer:

Microprocessor architecture, programming, and applications with the 8085 by Ramesh S. Gaonkar.

Giving brain to Computer

If someone has told you to create a brain, what will you do first? Is that so simple? Obviously not! If you want to create something that will coordinate the activities of the system will be a complicated task ever seen. The reason I wrote here that all we know the real brain of computer is a microprocessor. It is the most complicated part of the computer system. The logic behind computer system is in-built inside the microprocessor. Future engineers learn this logic in computer architecture but very few understand that.

The concept of giving brain to the computer system is basically originated by Jon Von Neumann in the mid of 20^th century. So he is well known as father of modern computer. The second person who is known as father of modern computing is Allen Turing. Before 1950, the computer and its parts were working independently as per their own different control. This was the reason why there was no coordination among these all parts of the computer system. How our human body works? None of the part of the human body has its own control mechanism. The overall coordination and control is given by human brain. Due to this, human body has a great coordination among all the parts of it. For example: we cannot keep our noses close continuously by putting our hands on it. It is just impossible! Just try it…!!! You can’t do that. This is only due to the coordination fetched inside the body and controlled by the brain. The same concept is adopted and applied to create a computer of new generation. Still today our computers work on this concept. The brain here is well known as Central Processing Unit or in short a CPU. We generally call it by microprocessor or just as processor. Neumann is the originator of this concept. He has shaped the idea of the computer is more specific manner. He is the real pioneer in the research of computing field.

He has not only given the design of the modern computer but also given the logic behind various activities that computer system does. Such as, computational, arithmetical, logical or data transfer activities. I always used to say that computer is not a magical machine it is a logical machine. At least engineers should have to think in this way. When the brain is given to the computer in the history its working efficiency was increased dramatically. Computer scientists made several necessary changes in the design of this brain. Today, we are seeing most advanced brains of the computer that is microprocessor. From the generation of 4 bit 4004 processor, we are now in multi-core generations and approaching towards optical and Nano processors. This is just the advancement of the generations.

This blog gives the look of these new technologies of the computing world including a ‘different’ brain of the computer that is ‘microcontroller’. When minimized tasks of the computer are required, this brain (generally small body) is used to drive the computer system. This blog will focus various aspects of microprocessor and microcontrollers used in the computing world today. Hope you will like that.