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# ABIT COMPUTER CORPORATION
AT420/AT425/AT433/AT450
Processor 80486SX/80486DX
Processor Speed 20/25/33/50MHz
Chip Set SIS
Max. Onboard DRAM 32MB
Cache 32/64/128/256/512/1024KB
BIOS AMI
Dimensions 330mm x 218mm
I/O Options None
NPU Options 4167
IMG IMG 1
+------------------------------------------------------------+
| CONNECTIONS |
|------------------------------------------------------------|
| Purpose | Location | Purpose | Location |
|---------------------+----------+----------------+----------|
| Speaker | CN1 | Turbo switch | JP1 |
|---------------------+----------+----------------+----------|
| Power LED & keylock | CN2 | Turbo LED | JP2 |
|---------------------+----------+----------------+----------|
| External battery | CN3 | Reset switch | SW1 |
+------------------------------------------------------------+
+------------------------------------------------------------+
| USER CONFIGURABLE SETTINGS |
|------------------------------------------------------------|
| Function | Jumper | Position |
|--------------------------------------+--------+------------|
| » | CMOS memory normal operation | JP5 | pins 1 & 2 |
| | | | closed |
|---+----------------------------------+--------+------------|
| | CMOS memory clear | JP5 | pins 2 & 3 |
| | | | closed |
|---+----------------------------------+--------+------------|
| » | Monitor type select monochrome | JP7 | Open |
|---+----------------------------------+--------+------------|
| | Monitor type select color | JP7 | Closed |
|---+----------------------------------+--------+------------|
| » | Factory configured - do not | JP8 | Open |
| | alter | | |
|------------------------------------------------------------|
| Note:Jumper JPX3 is closed using an 8-pin terminating |
| resistor. |
+------------------------------------------------------------+
+------------------------------------------------------------+
| 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 |
+------------------------------------------------------------+
+------------------------------------------------------------+
| CACHE CONFIGURATION |
|------------------------------------------------------------|
| Size | Bank 0 | Bank 1 | TAG | Location |
|--------+-------------+-------------+------------+----------|
| 32KB | (4) 8K x 8 | NONE | (1) 8K x 8 | T-1 |
|--------+-------------+-------------+------------+----------|
| 32KB | (4) 8K x 8 | (4) 8K x 8 | (2) 16K x | T-2 |
| | | | 4 | |
|--------+-------------+-------------+------------+----------|
| 64KB | (4) 8K x 8 | (4) 8K x 8 | (1) 8K x 8 | T-1 |
|--------+-------------+-------------+------------+----------|
| 64KB | (4) 8K x 8 | (4) 8K x 8 | (2) 16K x | T-2 |
| | | | 4 | |
|--------+-------------+-------------+------------+----------|
| 128KB | (4) 32K x 8 | NONE | (1) 8K x 8 | T-1 |
|--------+-------------+-------------+------------+----------|
| 128KB | (4) 32K x 8 | NONE | (2) 16K x | T-2 |
| | | | 4 | |
|--------+-------------+-------------+------------+----------|
| 256KB | (4) 32K x 8 | (4) 32K x 8 | (2) 16K x | T-2 |
| | | | 4 | |
|--------+-------------+-------------+------------+----------|
| 512KB | (4) 128K x | NONE | (1) 32K x | T-1 |
| | 8 | | 8 | |
|--------+-------------+-------------+------------+----------|
| 512KB | (4) 128K x | NONE | (2) 64K x | T-2 |
| | 8 | | 4 | |
|--------+-------------+-------------+------------+----------|
| 1024KB | (4) 128K x | (4) 128K x | (1) 128K x | T-1 |
| | 8 | 8 | 8 | |
|--------+-------------+-------------+------------+----------|
| 1024KB | (4) 128K x | (4) 128K x | (2) 64K x | T-2 |
| | 8 | 8 | 4 | |
+------------------------------------------------------------+
+------------------------------------------------------------+
| CACHE JUMPER CONFIGURATION |
|------------------------------------------------------------|
| Size | JP3 | JP4 | JPX4 | JPX5 |
|---------+---------+---------+----------------+-------------|
| 32KB | Open | Open | pins 1 - 8 | pins 1 - 8 |
| | | | closed | closed |
|---------+---------+---------+----------------+-------------|
| 64KB | Open | Open | pins 9 - 16 | pins 3 - 10 |
| | | | closed | closed |
|---------+---------+---------+----------------+-------------|
| 128KB | Open | Closed | pins 1 - 8 | pins 5 - 12 |
| | | | closed | closed |
|---------+---------+---------+----------------+-------------|
| 256KB | Open | Closed | pins 9 - 16 | pins 7 - 14 |
| | | | closed | closed |
|---------+---------+---------+----------------+-------------|
| 512KB | Open | Closed | pins 1 - 8 | pins 9 - 16 |
| | | | closed | closed |
|---------+---------+---------+----------------+-------------|
| 1024KB | Closed | Closed | pins 9 - 16 | pins 9 - 16 |
| | | | closed | closed |
|------------------------------------------------------------|
| Note:Jumpers JPX4 & JPX5 are closed using 8-pin |
| terminating resistors. |
+------------------------------------------------------------+
+------------------------------------------------------------+
| CACHE JUMPER CONFIGURATION |
|------------------------------------------------------------|
| Type | JP6 | JPX3 |
|--------------------+-------------------+-------------------|
| 80486SX | Closed | Open |
|--------------------+-------------------+-------------------|
| 80486DX | Open | Closed |
+------------------------------------------------------------+