Mr. Rodelio P. Barcenas
Faculty Computer Engineering Department
Don Bosco Technical College

The Intel 8085 microprocessor has 7 registers, A, B, C, D, E, H, L while M is a memory pointer. The codes you see at the leftmost side is what we call Op-Codes or simply machine codes.

Example:

47 MOV B,A {B <-- A}

47 is the machine code
MOV B,A is called the mnemonic
B <-- A is the RTL

The mnemonic is the easiest, simplest translation that can tell what the processor is doing. The processor cannot understand letters. To commmunicate to the processor, we have to know exactly what codes we want the processor to do. You can find these mnemonics if you are programming in Assembly Language. The RTL is a psuedo graphical representation of the mnemonic in case you don't easily understand the mnemonic.

If we try to relate our last example to the instruction set of the 8085 microprocessor, you can easily point out that the two are similar, except of course the codes. The example uses only a 4 bit control element while the 8085 is using 8 bits. An 8 bit control element can have 256 possible combinations or RTLs. Plus of course the size of the registers in an 8085 microprocessor, you can now imagine how complex the internal circuitry of this microprocessor. A 16 bit processor can have at least up to 65,536 possible instructions (RTLs). Complex? You bet.

At this point you should have an idea how these machine codes in microprocessors

About the RTLs and Op Codes

RTLs and registers are closely related to one another... If I have a register circuit at hand, there must be an RTL which will describe the register circuit. Taking it in reverse, if I have an RTL, I can construct a register circuit which will perform the given RTLs. Why do we need to talk about this?

If I were manufacturing a microprocessor, take the case of Intel. AMD, Cyrix, et al can manufacture their own processor as long as the codes and RTLs are exactly the same with Intel processors. Why? If their codes aren't the same, there would be software in-compatibility between them. If their codes are the same, software operating systems in Intel platform can also run in AMD or Cyrix. Get the idea? The other microprocessor can design their own register circuitry but the bottom line, the RTLs and codes in the end should be the same.

Microprocessors with different codes

Have you watched the movie " Independence Day"? It is about a story of earth invaded by aliens from outer-space. The aliens are too powerful with their arsenals and the people on earth is running out of chances. Every strategy doesn't even to affect the aliens. The movie is good to view if you are a amazed by the visual effects of the movie. At the end, a guy discovered that by planting a computer virus on the alien's mother-ship can disable their defenses. When their defenses are down, the earthlings can easilly mount an attack against the aliens. Well, they suceeded in planting a software virus on the alien's computer system. And as the story goes the earthlings defeated the aliens.

To think that aliens have a different computer system than ours, the probability that all of the codes of the aliens computer would be similar with that of the Intel is impossible. The aliens might be using Intel Computers. He he, just kidding.

I am not saying the movie is bad to watch or a non-sense, I am just looking at the technical point of view. I enjoyed watching the film, but just keep our secrets anyway. Its just between you and me.

On Computer Emulators...

Motorola is using a different architecture than Intel, meaning, different Codes and RTL compared to Intel. If you want to run a software running in Intel, Motorola should be executing an emulator software which will translate the codes of Intel into codes of Motorola. Because of these emulators, games under game consoles Play Station, Sega, Nintendo, Gameboy, etc can also be run in your own PCs.

On Processor Upgrade...

Naturally, we always want to improve almost everything in our lives. The 8085 has gone several changes even today, expect tomorow will be a new thing. The PCs are working much faster than before. Well, to tell you the truth, the Op Codes in lower types of microprocessor, were not changed. The codes remained the same, otherwise they will have to redo all the millions of wires inside the microprocessor. The manufacturers can only add new mnemonics, codes which will make a lenghty process before much simplier and faster.

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