From: joe@user.com   
      
    wrote in message   
   news:1159994577.204935.286400@h48g2000cwc.googlegroups.com...   
   > I hope someone can help me here... I'm a new owner of a "new" 1000HX,   
   > and want some more technical info on it. From the Tech manual for the   
   > original 1000, I found that the 1st 1000 had up to 2 wait states for   
   > RAM access, and 1 for I/O. Since HX is both faster at 7.16MHz and has   
   > no DMA as standard, what is the wait state situation on it?   
   >   
   > Also, when adding the memory card with the DMA chip on it, how exactly   
   > does it work? Is the DMA available to all memory now, or is it only for   
   > the additional memory added via the card?   
   >   
   > Thanks for any help!   
   >   
   > ScoutGSX   
   >   
      
   I'd have to find a tech manual to answer about the wait states, but here is   
   what I believe I remember.  (is that vague enough for you?)   
      
   The Tandy 1000 series generally operated the same across many variants.   
   That is, the base memory of the machine was 128K.  This memory was   
   SHARED and/or dual-mapped between the CPU main memory map   
   and the video.  That's why the wait states.  When you added more memory,   
   the added memory went in starting at 0000:0000 and the base memory   
   address got 'shoved up' to sit on 'top' of the new memory.  That way the   
   video access hardware didn't have to change, just the 'map' of how the   
   CPU got to the memory for generic CPU accesses.  While the systems   
   officially went to 640K (and still shared that top 128K with video), you   
   could actually trick it to bump the video up even further.   
      
   There was no DMA on a base 1000, at first.  Remember, it was really a   
   PC-jr on steroids to be 'business compatible'.  Without the first memory   
   upgrade, everything was polled.  Once the memory was added, then   
   the BIOS 'assumed' that the DMA was there and worked.  That brought   
   a lot of regular 1000 owners grief, as if the DMA didn't work, the   
   machine would boot without memory added, but die with memory.   
   Usually the problem wasn't the machines fault.  There was a voltage line   
   on the buss that was right next to one of the DMA pins.  On the regular   
   1000 with a card cage, if you pulled or inserted a card without letting the   
   power supply 'bleed down', and you 'cocked' the card at all putting it in   
   or taking it out, POP.  No more DMA.  On the discrete part 1000   
   motherboards it was an easy fix.  My brother trashed his, so at the time   
   I could easily get a 74LS06 at Radio Shack and 'piggy back' it right over   
   the original chip.  Since it blew the original chips output to an open, I   
   didn't even have to suck the old part off the board, I just left it in.   
      
   As to the IO waits, I believe there were additional waits.  The problem   
   was there were a lot of aftermarket I/O cards for the PC, and while a   
   lot of them would work in 6 and 8Mhz, there were a few that were real   
   dogs, so everybody had to slow down to work with them.  Yes, the   
   HX had a custom bus, but it was actually the 'same but different' as a   
   regular PC.  I just hung a small cardcage out the back of my Dad's HX   
   and ran cables out to it so he could run 3 standard PC cards.  And there   
   was even a company (I seem to recall Aconix (if that's spelled right) as   
   well as one other in West Virginia I think ) that sold 'expansion boxes'   
   for the HX.  The West Virginia company had hard drive kits for the   
   thing.  Aconix had one for the laptops that started to appear about that   
   time, but they also had a card for the HX.   
      
   Mike   
      
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