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Andy Neil
09/10/05 01:52
Read: 954 times

#100892 - If you want a proper answer...
Responding to: Neil Kurzman's previous message
Neil Kurzman said:
In any case You Need a general embedded or X86 embedded group.

Exactly - why would you expect an 8051 "expert" to answer detailed x86 questions?!

If he'd asked a proper, on-topic 8051 question, I'd have the "bible," data sheets etc to look it up and give a definitive (hopefully!) answer - all this x86 stuff is just from memory...

In X86 in ASM or a 'C' near pointer (a 'C' far pointer has no problem) if you inc a pointer set to 0xFFFF you end up at the bottem of the segment. so an increment at FFFF:FFFF gives you FFFF:0000 not 0000:0000.

That sounds right - because the 16-bit Offset rolls-over from FFFF to 0000 independently of the 16-bit Segment.

That's why I specifically chose the example of the 16-bit Offset incrementing from 000F to 0010, giving a 20-bit EA roll-over from FFFFF to 00000.
I think that's right, isn't it?

Of course, a joy of the Segmented architecture is that you're not restricted to rollover problems just at the end of memory - you can have a rollover at the end of any paragraph in memory...!

On X86 0000:0000 would not be the boot code. the reset vector is at the top of memory. It must have a jump the the start of code.
the bottom of memory for AM188 is the Interupt Vector Table.

Yes - see and

MOV@R0 on the '52 would give you similar results.

Not quite - PDATA pages in the 8051 do not overlap...

Anyhow, the OP seems to have lost interest now.

List of 16 messages in thread
Micro Controller powered?      Rupesh Deenadayalan      09/06/05 00:10      
   bible study time?      Andy Neil      09/06/05 01:22      
      Reboot ?      Rupesh Deenadayalan      09/08/05 00:53      
         See reply (Off-Topic)      Andy Neil      09/08/05 01:41      
   Not A PC      Neil Kurzman      09/06/05 09:35      
      Reboot doubt      Rupesh Deenadayalan      09/08/05 00:35      
         Off Topic.      Andy Neil      09/08/05 00:47      
            Rampant code execution      Andy Neil      09/08/05 01:00      
            CS:IP      Abhishek Singh      09/08/05 06:45      
               Irrelevant?      Andy Neil      09/08/05 08:47      
                  irrelevent: irrelevent?      Abhishek Singh      09/08/05 09:16      
                     TOTALLY irrelevant, at least at a '51 fo      Erik Malund      09/08/05 09:39      
                        Already established!      Andy Neil      09/08/05 10:37      
                     Wrong      Andy Neil      09/08/05 11:46      
                        You Sure?      Neil Kurzman      09/09/05 12:45      
                           If you want a proper answer...      Andy Neil      09/10/05 01:52      

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