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                           A2320 'Amber' Reference


  The A2320 is a video deinterlacer board originally built for the A2000. It
  is essentially the motherboard deinterlacer circuitry from the A3000 on a
  board. Based on the Amber chip used in the A3000, the board is often
  referred to as the Amber board. Physically, the board is designed to fit
  into the video slot of an A2000. Electronically, it works fine in an A4000.

  Why would you need a separate deinterlacer board when the A4000 already has
  AGA circuitry that can scan-double? If you have a VGA or multisync monitor,
  there are two main reasons:

  A. Not all programs can be mode-promoted to "double" screens through
     software (games, for instance). The Amber board will scan-double all
     15.75 kHz screens.

  B. The AGA "double" modes are not truly double in frequency. A 640x200
     "doubled" screen syncs at about 27.5 kHz, not the 31.5 kHz that you'd
     expect. Some multisync monitors can't sync this low. With an Amber
     board, the output is 31.5 kHz, the same as "stock" VGA.

  Physical Mounting

  A modified "slot cover" can be attached to the back panel of the Amber board
  to allow it to be attached securely to an A4000 slot. You'll also need to
  trim a bit off the "top" of the Amber's metal panel to allow clearance for
  the A4000 case (a nibbling tool is useful here). The board will only fill
  part of A4000 video slot; it looks funny this way, but it works.

  Don't remove the enable/disable switch! The Amber gets confused by some of
  the "doubled" screen modes, and rather than passing them through, tries to
  double them to 55 kHz or above! On these modes, you'll need the disable
  switch to force the board to pass the video through. (Productivity mode is
  passed through correctly, since it was part of the ECS chip set that was
  around when the Amber board first came out.)


  The Amber board was designed before AGA came out, and doesn't really under-
  stand AGA. As noted above, some modes are not passed through properly
  unless the board is disabled with the switch. According to Scott Hood, the
  designer of the A2320, it samples 12 bits for each color. On the A4000,
  this is the upper 12 bits of the 24-bit AGA information. So AGA screens
  with more than 32 colors or HAM-6 will have the colors quantized to a
  certain degree. This hasn't been a problem so far, although it can be seen
  on things like ImageFX preview screens. Games that use the AGA color
  abilities but don't allow for promoting their screens to doubled modes are
  the only likely sources for this trouble.

Converted on 02 Jun 1997 with RexxDoesAmigaGuide2HTML 2.1 by Michael Ranner.