A4000 Motherboard Jumpers

                              Motherboard Jumpers

-----------------------------------------------------------------------------


 A4000 Motherboard

   ------------------------------------------------
  |   ooo            || oo           |             |
  |  Internal        || DF1:         |             |
  |  Audio           || Enable       |             |
  |  Connector       ||              |    Power    |
  |                  ||              |    Supply   |
  |  :: Mystery      ||              |             |
  |  :: Header       ||          ooo |             |
  |  :: (see below)  ||          ooo |     Fan     |
  |                  ||          ooo  -------------|
  |                  ||         Power Supply       |
  |                  ||         Connector          |
  |                  ||                            |
  |                  ||         -------------------|
  |                  ||        |                   |
  |                  ||        |                   |
  |                  ||        |                   |
  |                  ||        |       Drive       |
  |                  ||        |       Bays        |
  |                  || oo     |                   |
  |                  || SIMM   |                   |
  |                  || Size   |                   |
  |                  ||        |                   |
   ------------------------------------------------

  Jumpers

    J351: DF1 Enable
          Closed: Enable low-density (880K) floppy as DF1.
          Open:   No DF1 *OR* for high-density (1.76M) DF1.

    J852: Fast RAM SIMM Size (Chip RAM is always 2M.)
          256K: 1M SIMMs.
          1M  : 4M SIMMs.

    CN404: Internal Audio Connector
           Audio signals attached here will be mixed with the A4000 audio
           output. The A4000 audio is somewhat louder than the normal line
           level output from most CD-ROM drives, presumably to make sound
           effects audible over background music. Setting the software-
           controlled A4000 audio level lower (to 32 instead of 64) will help
           match the levels.

      Pin 1: Audio In (Left)
      Pin 2: Ground.
      Pin 3: Audio In (Right)

  "Mystery" Header (courtesy of Dave Haynie)

  "There is a 12 pin header (DIL, J975) near the mouse ports. This feeds the
  'extra' shift register in Lisa. Unlike OCS/ECS systems, which simply
  multiplex the four quadrature signals from each mouse port with one
  another, the AA systems serialize all eight bits of mouse data. While they
  were at it, the AA designers added a second 8-bits to the mouse port
  registers. These don't hook into mouse logic or anything, but they can be
  read by the CPU.

  So we used them for configuration. The first two bits (not on that header)
  tell the OS about the AA system -- is it 16 or 32 bit, is it single or
  double access per cycle. These are hard-wired on the motherboard. The
  remaining six bits read high when unjumpered, low when jumpered. I had
  recommended using one to say 'VGA only,' but there wasn't enough ROM
  space."

  Other Jumpers (Not Shown Above)

    J100: CLK90 Clock Source
          1-2 Closed: Internal (68020/68030)
          2-3 Closed: External (68040)

    J104: CPU Clock Source
          1-2 Closed: Internal
          2-3 Closed: External

    J151: ROM Speed: 160 or 200 ns ROMs.
          1-2 Closed: 200 ns ROMs (default).
          2-3 Closed: 160 ns ROMs.

    J213: Chip RAM: 2M or 8M
          1-2 Closed: 2M Chip RAM (default).
          2-3 Closed: 8M Chip RAM. This option was apparently for use
                      with the never-released AAA chip set, and won't
                      work in a normal A4000.

    J500: Sync On Green
          1-2 Closed: Sync on green disabled (default?).
          2-3 Closed: Sync on green enabled

    J501: Lisa Sync (Wide input on the Lisa chip.)
          1-2 Closed: CSync from Agnus Pin 80.
          2-3 Closed: +5V (default).

    J502: Select DAC Sync
          1-2 Closed: DAC syncs on green.
          2-3 Closed: DAC uses standard signal (default).

    J850: Enable DSACK (Used with 68020)
          1-2 Closed: DSACK Enabled for 68020. U860 and U152 also required.
          2-3 Closed: No DSACK.

    "Haynie Kludge" Jumper (courtesy of Dave Haynie)

    "That jumper enables the "early sizing" mode on the Zorro III bus. One
    of the complaints about Zorro III is that the size of a transfer isn't
    known until the data phase of the cycle. So in the Zorro III addendum I
    added an optional mode that allows data size information to be latched in
    the address phase. Just in case any existing boards have a problem with
    this (if they go by the spec, they don't, but who really knows what
    they're doing), it's shipped disabled. The idea was to test this out in
    the A4000T, bless it as standard for future Zorro III controllers as long
    as it did what designers wanted."