[Coco] assembly language question.

[Gene Heskett]

On Wednesday 03 February 2010, Bob Devries wrote:
>The 6809 CMP instruction can be either 8 bit or 16 bit. For 16 bit the
>operation is: (quote)
>
>Compares the 16-bit contents of the concatenated memory locations M:M+1 to
>the contents of the specified register and sets the appropriate condition
>codes. Neither the memory locations nor the specified register is modified
>unless autoincrement or autodecrement are used. The carry flag represents a
>borrow and is set to the inverse of the resulting binary carry.
>
>(/quote)
>
Page A-33, moto's Silver book.  My copy (May '83 edition) is a slight bit 
yellowed after all these years. ;)

That, as the Genesis book for all of this, really could have been written a 
wee bit clearer, IMO.

In particular, I detest the RPN style notation used there and it would be a 
lot less ambiguous to me had the shorthand been stated algebraic style:

R-[M:M+1] -> CC(NZVC)

The left to right order is the correct order of the occurrence's within the 
nemonics operation.


Thanks Bob.

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)

If you can't understand it, it is intuitively obvious.