Require some dumbed down definitions

[+Random Terrain]

Does anyone have simple definitions for the following two things:

 

not 'orthogonal'

So far, we have seen that what we can do with all the registers is essentially the same. Unfortunately, this is not the case with all the addressing modes! The 6502 is not 'orthogonal' - and this has some bearing on our choice of which register to use for which purpose, when designing our kernel.

 

 

non-orthogonality

That last line is interesting - an example of the non-orthogonality of our instruction set.

 

 

 

 

Thanks.

 

 

Edited April 15, 2011 by Random Terrain

[ScumSoft]

Has no intersecting lines, nor right angles?

 

[edit] In that case then "Has both direct and indirect addressing modes"

But I can't think of an way to explain both this and what direct and indirect modes do at the same time.

 

Direct addressing grabs a value straight from the address.

Indirect grabs the address from the address...then the value

 

lda Number     = Number is a memory address which holds (5)
lda Number,Y   = Address of Number+Y (Y = 0-255) and returns value stored at Number+Y
lda (Number)   = Number holds an address not a direct value, so it returns an address which points to the value.
lda (Number),Y = Same as above but returns (Address) then Number+Y

 

Hmmm, going from memory here so I might have gotten this wrong

Edited April 15, 2011 by ScumSoft

[+Random Terrain]

Has no intersecting lines, nor right angles?

Oops, I just added the context in my post so the meaning would be clear.

[Ed Fries]

It's a fancy word you can easily do without. All he is trying to say is that the registers aren't all equal. Some operations require certain registers. For example you can only do math with the A register. If you want to set the stack pointer you have to use the X register (TXS instruction. There is no TYS or TAS.) Etc. There are many examples.

 

I like to use this: 6502 opcodes to figure out what I can and can't do.

[ScumSoft]

Oh, that makes sense.

Thought it was referring to addressing modes for data. Learn something new every day

[+Random Terrain]

It's a fancy word you can easily do without. All he is trying to say is that the registers aren't all equal. Some operations require certain registers. For example you can only do math with the A register. If you want to set the stack pointer you have to use the X register (TXS instruction. There is no TYS or TAS.) Etc. There are many examples.

 

I like to use this: 6502 opcodes to figure out what I can and can't do.

Thanks. This is the exact kind of info I'm looking for.

[Glade Swope]

If there's "No OPeration", how can there be an operand?

 

"Do nothing to the accumulator."

 

What about the three-cycle NOP?

[ScumSoft]

My benevolent Atari gods, why did you resurrect this infernal thread!?

 

NOP is an instruction, NOP #0 is an instruction with a parameter.

NOP can take parameters but will not do any work on them, instead it simply is burning cycle time as it parses over them.

 

A = A is an assignment which makes the point that something is being done, but nothing has actually been done.

This is why NOP can be considered an Operator and Operand.

 

NOP <--Operator by itself

NOP #0 <--Operator told to work on a byte and do something different, thus working as an Operand

[+nanochess]

Of course take note that NOP #0 is an undocumented instruction and it could fail in some Atari variations like the Flashback.

[Keatah]

Maybe people should put forth some effort and learn how to learn something. Forget this silver-spoon feeding approach.

[+Gemintronic]

Maybe people should put forth some effort and learn how to learn something. Forget this silver-spoon feeding approach.

 

The approach you're suggesting works to a point. I've had plenty of dipsticks in my life that have almost killed my curiosity by withholding information.

[Keatah]

Well those dipsticks are assholes to be sure I'm sure..

[John_L]

If you want your readers to understand what is meant when saying "operand", it should mean finding a simple definition that explains what is going on with an example then relating that definition to the jargon word that is commonly used, covers both avenues. Understanding what is going on and supplying one word that labels the concept. That word being agreed upon by the general consensus.

 

I got one for ya: (j/k)an Operand is the part of a computer command that is worked on and becomes the result of the command.

 

Example: A=A+1

In the example, the + represents the command or opcode being done

The A is the operand it is done to.

And the 1 is the operand it is done with.

Addition is not an opcode. An opcode is a numeric value that the CPU treats as an instruction....

 

it's quite simple. operation

|

1 + 1 = 2 <--- result.

operand ^ ^operand