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???
09/20/07 20:36
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 		 #144847 - mhm
Responding to: ???'s previous message
Maarten Brock said:
Jan, your version would mean to me:

JMP (@A) + DPTR ;get the value at the address stored at A (in which memory?), add it to DPTR and jump to it.


Quite so.

But the reason for this notation is historical, and - not too surprisingly - it comes from the 8048 instruction set. The indirect jump, JMPP @A, took content of A, looked up value on the current page pointed by A, and placed that instead of low portion of PC. This is a true indirection, unlike in the JMP @A+DPTR in '51. However, I bet, the designers of '51 wanted to stress the continuity; and as MOVP A,@A and MOVP3 A,@A mapped quite straghtforwardly into MOVC A,@A+PC and MOVC A,@A+DPTR, they assumed a similar analogy for the "table jump", too, even if it works in a different manner.

JW

List of 62 messages in thread
TopicAuthorDate
weekend survey            01/01/70 00:00      
   1. programming through the whole night            01/01/70 00:00      
   two things at once            01/01/70 00:00      
      not entirely correct            01/01/70 00:00      
   I'm afraid, but...            01/01/70 00:00      
      stealing codes?            01/01/70 00:00      
         A lesson learned by many            01/01/70 00:00      
         They are way faster...            01/01/70 00:00      
            sounds like a bitter experience            01/01/70 00:00      
   3)Math            01/01/70 00:00      
      0) Math            01/01/70 00:00      
   I have to agree with Erik            01/01/70 00:00      
   For hardware design(VHDL)            01/01/70 00:00      
      then, throw out the crap            01/01/70 00:00      
   Math, experience, tools and code libraries            01/01/70 00:00      
   Why?            01/01/70 00:00      
      tradeoffs            01/01/70 00:00      
         Well said, but not what I asked            01/01/70 00:00      
            different question            01/01/70 00:00      
               technique v tool            01/01/70 00:00      
      two reasons            01/01/70 00:00      
         valuation            01/01/70 00:00      
            that's a given, but            01/01/70 00:00      
            Lookup tables are good for lots of stuff            01/01/70 00:00      
   Good topic!            01/01/70 00:00      
      common tool, but            01/01/70 00:00      
         Function Pointers on the 8051            01/01/70 00:00      
            table-driven whatever and function pointers            01/01/70 00:00      
               reduce a task to its basic elements            01/01/70 00:00      
                  Good idea, bad example            01/01/70 00:00      
                     I didn't really want to use 805x instructions            01/01/70 00:00      
                        I can\'t find my old, (t)rusty 65C02 cheatsheet...            01/01/70 00:00      
                           Only the Rockwell version had it            01/01/70 00:00      
                              Oh, mea culpa...            01/01/70 00:00      
                        A very simple example would be helpful            01/01/70 00:00      
                           let\\\'s start at your end            01/01/70 00:00      
                              Here's what's confusing            01/01/70 00:00      
                                 FAQ?            01/01/70 00:00      
                                 Yes, you're quite right ... ... Mea culpa            01/01/70 00:00      
                  inconsistent instruction set            01/01/70 00:00      
                     I ask you, seriously, to inform us            01/01/70 00:00      
                        a few things            01/01/70 00:00      
                           so much \'fun\' with ajmp            01/01/70 00:00      
                              I give up            01/01/70 00:00      
                                 the answer            01/01/70 00:00      
                           My intuition            01/01/70 00:00      
                              mhm            01/01/70 00:00      
      to russ            01/01/70 00:00      
         to erik            01/01/70 00:00      
            to Russ            01/01/70 00:00      
               to Erik            01/01/70 00:00      
               To Erik            01/01/70 00:00      
                  WOW, a companion CD            01/01/70 00:00      
   the bad ideas            01/01/70 00:00      
      Anachronism?            01/01/70 00:00      
         he's certainly not a HW guy...            01/01/70 00:00      
      Hardware protection slated            01/01/70 00:00      
         this is an academic view...            01/01/70 00:00      
            Proving correctness            01/01/70 00:00      
   Why state machine / lookup tables?            01/01/70 00:00      
      Not to disagree ... but ...            01/01/70 00:00      
         A good reference            01/01/70 00:00      

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