
ABIT COMPUTER CORPORATION

AV4 VL-BUS MAIN BOARD

Processor            80486SX/80487SX/80486DX/80486DX2
Processor Speed      20/25/33/50(internal)/50/66(internal)MHz
Chip Set             SIS
Max. Onboard DRAM    32MB
SRAM Cache           64/128/256KB
BIOS                 AMI
Dimensions           220mm x 254mm
I/O Options          32-bit VESA card slot (2)
NPU Options          None

[Image]

                                CONNECTIONS

  Purpose                Location      Purpose                 Location

  Keylock                  CN1         External battery          CN6

  Speaker                  CN3         Reset                     CN8

  Turbo LED                CN4         Power LED                 LED1

  Turbo switch        CN5/pins 2 & 3   32-bit VESA card        S1 & S2
                                       (2)

                        USER CONFIGURABLE SETTINGS

                Function                     Jumper          Position

     VESA bus speed select 20/25/33MHz    JP8 and JP10      pins 1 & 2
                                                              closed

      VESA bus speed select 50MHz          JP8 and JP10      pins 2 & 3
                                                              closed

     VESA bus wait state select 1         JP9 and JP11      pins 1 & 2
                                                              closed

      VESA bus wait states select 0        JP9 and JP11      pins 2 & 3
                                                              closed

     CMOS memory normal operation            JP12           pins 1 & 2
                                                              closed

      CMOS memory clear                       JP12           pins 2 & 3
                                                              closed

     Fast gate A20 select enabled            JP17           pins 1 & 2
                                                              closed

      Fast gate A20 select disabled           JP17           pins 2 & 3
                                                              closed

     Monitor type select color               JP18            closed

      Monitor type select monochrome          JP18             open

     Factory configured - do not alter       JP23           See note
      1

     Factory configured - do not alter       JP24           See note
      1

     Factory configured - do not alter       JP25           See note
      1

     Factory configured - do not alter       JP26           pins 2 & 3
      1                                                       closed

     Factory configured - do not alter       JP27           pins 2 & 3
                                                              closed

     Factory configured - do not alter       JP28           See note
      1

  Note:The locations of JP23, JP24, and JP25 are unknown

  Note 1 :JP23 through JP28 are set at the factory depending on whether
  the R1 or R2 Model is shipped.

              DRAM CONFIGURATION

      Size          Bank 0          Bank 1

      1MB         (4) 256K x 9       NONE

      2MB         (4) 256K x 9   (4) 256K x 9

      4MB         (4) 1M x 9         NONE

      8MB         (4) 1M x 9      (4) 1M x 9

      16MB        (4) 4M x 9         NONE

      32MB        (4) 4M x 9      (4) 4M x 9

                            SRAM CONFIGURATION

    Size     Cache SRAM     Location         TAG(U14)         TAG(U15)

    64KB     (8) 8K x 8    Banks 0 & 1      (1) 8K x 8       (1) 8K x 8

   128KB      (4) 32K x      Bank 0         (1) 8K x 8       (1) 8K x 8
                 8

   256KB      (8) 32K x    Banks 0 & 1      (1) 32K x 8     (1) 32K x 8
                 8

  Note:If SRAM is installed at U15 then write-back caching is enabled.

  If SRAM is installed at U14 and U15 then write-back or write-through
  caching can be enabled.

                         SRAM JUMPER CONFIGURATION

      Jumper             64KB              128KB              256KB

       JP1            pins 1 & 2         pins 2 & 3         pins 2 & 3
                        closed            closed             closed

       JP2            pins 1 & 2         pins 1 & 2         pins 2 & 3
                        closed            closed             closed

       JP3            pins 1 & 2         pins 2 & 3         pins 2 & 3
                        closed            closed             closed

       JP4            pins 1 & 2         pins 1 & 2         pins 2 & 3
                        closed            closed             closed

       JP5            pins 2 & 3         pins 1 & 2         pins 2 & 3
                        closed            closed             closed

       JP6            pins 1 & 2         pins 1 & 2         pins 2 & 3
                        closed            closed             closed

       JP7            pins 1 & 2         pins 2 & 3         pins 2 & 3
                        closed            closed             closed

                         CPU JUMPER CONFIGURATION

          CPU              Jumper       Jumper       Jumper      Jumper
                           JP13          JP14        JP15         JP16

   80486DX/80486DX2      pins 1 & 2   pins 1 & 2    closed       closed
                          closed        closed

        80487SX          pins 2 & 3   pins 1 & 2    closed       closed
                          closed        closed

     80486SX (PGA)         open       pins 2 & 3     open        closed
                                        closed

    80486SX (PQFP)         open       pins 2 & 3     open         open
                                        closed

                  CPU SPEED CONFIGURATION

     Speed      Jumper JP20    Jumper JP21    Jumper JP22

     20MHz         closed         closed         open

     25MHz         closed          open         closed

     33MHz          open          closed        closed

     50MHz          open          closed         open

