
TANDY/RADIO SHACK

425SX/T, 433SX/T, 433DX/T, 450DX2/T, 466DX2/T

Processor      80486SX/ODP486SX/80487SX/80486DX/ODP486SX/80486DX2
Processor      25/33/50(internal)/66(internal)MHz
Speed
Chip Set       Unidentified
Video Chip Set Unidentified
Maximum        40MB
Onboard Memory
Maximum Video  1MB
Memory
Cache          64/128/256KB
BIOS           Phoenix
Dimensions     330mm x 218mm
I/O Options    Floppy drive interface, IDE interface, parallel port, PS/2
               mouse port, serial ports (2), VGA feature connector, VGA
               port, riser slot
NPU Options    None

[Image]

                                CONNECTIONS

  Purpose                   Location   Purpose                   Location

  VGA port                    CN1      Reset switch                CN8

  Parallel port               CN2      External battery            J7

  Serial port 1               CN3      IDE interface               J17

  Serial port 2               CN4      Floppy drive interface      J18

  PS/2 mouse port             CN5      VGA feature connector       J21

  IDE interface LED           CN6      Riser slot                  SL1

  Power LED & keylock         CN7

                        USER CONFIGURABLE SETTINGS

                Function                     Label           Position

     Factory configured - do not alter        J9           Pins 1 & 2
                                                              closed

     Factory configured - do not alter       J11              Open

     Factory configured - do not alter       J13           Pins 1 & 2
                                                              closed

     Factory configured - do not alter       J14           Pins 2 & 3
                                                              closed

     CMOS memory normal operation            J20             Closed

      CMOS memory clear                       J20              Open

     On board video enabled                  J28           Pins 2 & 3
                                                              closed

      On board video disabled                 J28           Pins 1 & 2
                                                              closed

     Factory configured - do not alter       J29              Open

     Floppy drive write protect              J30           Pins 2 & 3
      disabled                                                closed

      Floppy drive write protect              J30           Pins 1 & 2
      enabled                                                 closed

     Factory configured - do not alter       J31           Pins 2 & 3
                                                              closed

     Zero wait state enabled                 J32             Closed

      Zero wait state disabled                J32              Open

                        DRAM CONFIGURATION

      Size            Bank 0           Bank 1          Bank 2

       1MB        (1) 256K x 36         None            None

       2MB             None         (4) 256K x 9    (4) 256K x 9

       2MB        (1) 512K x 36         None            None

       4MB             None          (4) 1M x 9         None

       4MB         (1) 1M x 36          None            None

       5MB             None          (4) 1M x 9     (4) 256K x 9

       6MB        (1) 512K x 36      (4) 1M x 9         None

       8MB         (1) 1M x 36       (4) 1M x 9         None

       8MB         (1) 2M x 36          None            None

       8MB             None          (4) 1M x 9      (4) 1M x 9

      10MB        (1) 512K x 36      (4) 1M x 9      (4) 1M x 9

      12MB         (1) 1M x 36       (4) 1M x 9      (4) 1M x 9

      12MB         (1) 2M x 36       (4) 1M x 9         None

      16MB         (1) 2M x 36       (4) 1M x 9      (4) 1M x 9

      16MB             None          (4) 4M x 9         None

                    DRAM CONFIGURATION (CONT)

      Size            Bank 0           Bank 1          Bank 2

      17MB             None          (4) 4M x 9     (4) 256K x 9

      18MB        (1) 512K x 36      (4) 4M x 9         None

      20MB         (1) 1M x 36       (4) 4M x 9         None

      20MB             None          (4) 4M x 9      (4) 1M x 9

      22MB        (1) 512K x 36      (4) 4M x 9      (4) 1M x 9

      24MB         (1) 1M x 36       (4) 4M x 9      (4) 1M x 9

      24MB         (1) 2M x 36       (4) 4M x 9         None

      28MB         (1) 2M x 36       (4) 4M x 9      (4) 1M x 9

      32MB             None          (4) 4M x 9      (4) 4M x 9

      34MB        (1) 512K x 36      (4) 4M x 9      (4) 4M x 9

      36MB         (1) 1M x 36       (4) 4M x 9      (4) 4M x 9

      40MB         (1) 2M x 36       (4) 4M x 9      (4) 4M x 9

                            CACHE CONFIGURATION

     Size          Bank 0       Bank 1           TAG              U1

     64KB        (4) 8K x 8   (4) 8K x 8      (1) 8K x 8     (1) 64K x 1

     128KB       (4) 32K x 8     None       (1) 8K/32K x 8   (1) 64K x 1

     256KB       (4) 32K x 8  (4) 32K x 8    (1) 32K x 8     (1) 64K x 1

                        CACHE JUMPER CONFIGURATION

                Size                                 J16

                None                   Pins 1 & 2, 3 & 4, 5 & 6, 9 & 10
                                                    closed

                64KB                                 Open

               128KB                   Pins 1 & 2, 5 & 6, 7 & 8 closed

               256KB                   Pins 1 & 2, 3 & 4, 5 & 6, 9 & 10
                                                    closed

                  VIDEO MEMORY CONFIGURATION

        Size                Bank 0               Bank 1

        512KB               512KB                 None

         1MB                512KB                512KB

  Note: The size of the video memory chips are unidentified.

                     CPU SPEED SELECTION

        Speed                J26                  J27

        25MHz          Pins 1 & 2 closed   Pins 2 & 3 closed

        33MHz          Pins 1 & 2 closed   Pins 1 & 2 closed

       50iMHz          Pins 1 & 2 closed   Pins 2 & 3 closed

       66iMHz          Pins 1 & 2 closed   Pins 1 & 2 closed

                   CPU TYPE SELECTION

            Type                        J19

          80486SX            Pins 1 & 3, 2 & 4 closed

          ODP486SX           Pins 1 & 3, 2 & 4 closed

          80487SX            Pins 1 & 3, 2 & 4 closed

          80486DX            Pins 3 & 5, 4 & 6 closed

          ODP486DX           Pins 3 & 5, 4 & 6 closed

          80486DX2           Pins 3 & 5, 4 & 6 closed

