[HN Gopher] Reverse-engineering the 8086 processor's address and...
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       Reverse-engineering the 8086 processor's address and data pin
       circuits
        
       Author : picture
       Score  : 87 points
       Date   : 2023-07-08 16:17 UTC (6 hours ago)
        
 (HTM) web link (www.righto.com)
 (TXT) w3m dump (www.righto.com)
        
       | nativeit wrote:
       | I'm going to leave smarter inquiries to those more qualified to
       | raise them, but I wanted to take a moment to express my
       | admiration and gratitude for your work in preserving, expanding,
       | and advancing our collective knowledge and understanding of low-
       | level computing and systems architecture. Hats off to you, it's
       | been incredibly rewarding to watch your work.
        
         | kens wrote:
         | Thanks! I'm trying to do what I can to preserve this history
         | and knowledge.
        
       | Stratoscope wrote:
       | Great article as always! I especially like the section on "A
       | historical look at pins and timing".
       | 
       | Unless I'm misunderstanding the terminology, there may be an
       | error in the discussion of the shift/crossover circuit. And a
       | minor typo...
       | 
       | > _The [buses] can be connected in three ways: direct, crossed-
       | over, or swapped._
       | 
       | > _The "direct" mode connects the 16 bits of the C bus to the
       | lower 16 bits of the address/data pins._
       | 
       | > _The second mode performs the same connection but swaps the
       | bytes._
       | 
       | > _The final mode shifts the 20-bit AD bus value four positions
       | to the right._
       | 
       | It sounds like those two modes got swapped? ;-)
       | 
       | For clarity, I think I would change the order in the introduction
       | and use the mode names instead of "second" and "final":
       | 
       | > _The buses can be connected in three ways: direct, swapped, or
       | crossed-over._
       | 
       | > _The "direct" mode connects the 16 bits of the C bus to the
       | lower 16 bits of the address/data pins._
       | 
       | > _The "swapped" mode performs the same connection but swaps the
       | bytes._
       | 
       | > _The "crossed-over" mode shifts the 20-bit AD bus value four
       | positions to the right._
        
         | kens wrote:
         | Thanks, I've fixed that section since I kind of mangled it.
        
       | kens wrote:
       | Author here if anyone has questions.
        
         | java-man wrote:
         | Thank you so much for your work! Always great fun to read your
         | blog.
        
       | mmastrac wrote:
       | How far are we away from a true transistor or gate-level
       | simulation of 8086/8088?
        
         | kens wrote:
         | I have a transistor-level 8086 simulator that mostly works but
         | needs some cleanup and bug fixes. For now, I'm concentrating on
         | analysis of the 8086 rather than finishing the simulator.
        
           | mmastrac wrote:
           | That's cool! Is it helpful for your analysis?
        
             | kens wrote:
             | Yes, the simulator is extremely helpful for analysis. I
             | started doing the analysis on paper, but it's very easy to
             | make a mistake and end up confused. The simulator is also
             | very helpful when trying to understand complicated state
             | machines such as the bus control circuitry. So I plan to
             | put more emphasis on simulation for future projects. The
             | tradeoff is that it takes a lot more time up front to get
             | the simulation working.
        
               | [deleted]
        
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       (page generated 2023-07-08 23:00 UTC)