Seagate ST21M/21R, & ST22M/22R MFM & RLL Controllers

View of the Controller.
  • J1: Floppy Drive Connector (ST22M/ST22R only)
  • J2: Hard Drive Control Connector
  • J3: Hard Drive #0 Data Connector
  • J4: Hard Drive #1 Data Connector
  • J5: Aux. Power Connector
  • J6: Hard Drive LED
    • Default settings are in Bold or are selected by a (Default) or (Optional)
    (JP1/JP2): BIOS & PORT Addresses
    I/O Port (JP1) (JP2) BIOS Addr. HD I/O Ports FD I/O Ports
    Primary Off Off C8000h-
    CBFFFh    		 1F0-1F7
    3F6-3F7    		 3F0-3F5
    3F7
    Off On CC000h-
    CFFFFh    		 1F0-1F7
    3F6-3F7    		 3F0-3F5
    3F7
    Secondary On Off D8000h-
    DBFFFh    		 170-177
    376-377    		 370-375
    377
    On On DC000h-
    DFFFFh    		 170-177
    376-377    		 370-375
    377
    (Default Address is C8000h.)

    JP3: BIOS Enable

  • (Default Setting): Open to Enable the BIOS.
  • (Optional Setting): Jumper to Disable the BIOS.

    • JP4: Floppy Support (ST22 Only)

  • (Default Setting): Jumper to Enable Floppy Support.
  • (Optional Setting): Open to Disable Floppy Support.

    • CMOS Settings
    Drive BIOS Address CMOS Setting
    BIOS
    Enabled    		 C: Primary
    I/O    		 C8000 or
    CC000    		 Set to Type#0 or
    C/H/S Specs.
    D: C8000 or
    CC000    		 Set to
    Not Installed
    C: or D: Secondary
    I/O    		 D8000 or
    DC000    		 Set to
    Not Installed
    BIOS
    Disabled    		 C: or D: Must be
    Primary    		 Set to C/H/S
    Specifications

    Notes:
  • The ST21/22 must be the Primary controller when used with the BIOS disabled.
  • Systems using a Motherboard ATA controller must usually have that interface disabled before an ST21/22 can be used.
  • The ST21/22 can coexist with many ATA controllers provided the BIOS is enabled, and set to the Secondary address.
    • The ST21/22 has a Low Level Formatter Utility built into it's BIOS. It is accessed by using the DOS Debug command at an offset of 5, as in...
    C:\debug <enter>
    -g=c8000:5 <enter>

    ... Where c8000 is the BIOS address. You may also use a 3rd Party software formatting utility.
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