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                                     

<gopher://bitreich.org/I/th99/m/S-T/35060-1.png>
   

   +------------------------------------------------------------+
   |                        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 | 32-bit VESA card    | S1 & S2  |
   |              |    & 3     | (2)                 |          |
   +------------------------------------------------------------+

   +------------------------------------------------------------+
   |                 USER CONFIGURABLE SETTINGS                 |
   |------------------------------------------------------------|
   |              Function              |  Jumper  |  Position  |
   |------------------------------------+----------+------------|
   |>>  | VESA bus speed select         | JP8 and  | pins 1 & 2 |
   |    | 20/25/33MHz                   |   JP10   |   closed   |
   |----+-------------------------------+----------+------------|
   |    | VESA bus speed select 50MHz   | JP8 and  | pins 2 & 3 |
   |    |                               |   JP10   |   closed   |
   |----+-------------------------------+----------+------------|
   |>>  | VESA bus wait state select 1  | JP9 and  | pins 1 & 2 |
   |    |                               |   JP11   |   closed   |
   |----+-------------------------------+----------+------------|
   |    | VESA bus wait states select 0 | JP9 and  | pins 2 & 3 |
   |    |                               |   JP11   |   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           |   JP18   |    open    |
   |    | monochrome                    |          |            |
   |----+-------------------------------+----------+------------|
   |>>  | Factory configured - do not   |   JP23   |  See note  |
   |    | alter 1                       |          |            |
   |----+-------------------------------+----------+------------|
   |>>  | Factory configured - do not   |   JP24   |  See note  |
   |    | alter 1                       |          |            |
   |----+-------------------------------+----------+------------|
   |>>  | Factory configured - do not   |   JP25   |  See note  |
   |    | alter 1                       |          |            |
   |----+-------------------------------+----------+------------|
   |>>  | Factory configured - do not   |   JP26   | pins 2 & 3 |
   |    | alter 1                       |          |   closed   |
   |----+-------------------------------+----------+------------|
   |>>  | Factory configured - do not   |   JP27   | pins 2 & 3 |
   |    | alter                         |          |   closed   |
   |----+-------------------------------+----------+------------|
   |>>  | Factory configured - do not   |   JP28   |  See note  |
   |    | alter 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) 8K x 8  | (1) 8K x 8 |
   |        |            |     1     |             |            |
   |--------+------------+-----------+-------------+------------|
   | 128KB  | (4) 32K x  |  Bank 0   | (1) 8K x 8  | (1) 8K x 8 |
   |        |     8      |           |             |            |
   |--------+------------+-----------+-------------+------------|
   | 256KB  | (8) 32K x  | Banks 0 & | (1) 32K x 8 | (1) 32K x  |
   |        |     8      |     1     |             |     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 & | pins 1 & | closed  | closed  |
   |                  | 2 closed | 2 closed |         |         |
   |------------------+----------+----------+---------+---------|
   |     80487SX      | pins 2 & | pins 1 & | closed  | closed  |
   |                  | 3 closed | 2 closed |         |         |
   |------------------+----------+----------+---------+---------|
   |  80486SX (PGA)   |   open   | pins 2 & |  open   | closed  |
   |                  |          | 3 closed |         |         |
   |------------------+----------+----------+---------+---------|
   |  80486SX (PQFP)  |   open   | pins 2 & |  open   |  open   |
   |                  |          | 3 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      |
   +------------------------------------------------------------+