Apple II Technical Notes _____________________________________________________________________________ Developer Technical Support UniDisk 3.5 #4: Accessing Macintosh Disks Revised by: Matt Deatherage November 1988 Written by: Mike Askins May 1985 This Technical Note formerly discussed drive-specific SmartPort calls. These calls are now documented in the Apple IIGS Firmware Reference. This Note now describes how to access Macintosh disks from a UniDisk 3.5 disk drive, as this information was not documented in the manual. _____________________________________________________________________________ Macintosh Disk Access The disk data format used in the UniDisk 3.5 is essentially identical to that used for Macintosh disks. There are three notable differences between the two formats: o Macintosh blocks are 524 bytes; UniDisk 3.5 blocks are 512 bytes. o Macintosh MFS disks are single sided; UniDisk 3.5 disks are double sided. (Macintosh HFS disks are double sided.) o The Macintosh uses a 2:1 physical block interleave; the UniDisk 3.5 uses a 4:1 interleave. Accessing Blocks on a Macintosh Disk Reading from a Macintosh disk is accomplished with the use of the READ command (as opposed to the READBLOCK command, which enforces 512 byte data.) A call to load block zero from the Macintosh disk in Unit #1 into memory at $2000 would look like this: MacRead JSR Dispatch ;Normal SmartPort Entry point DFB $08 ;Character READ command code DW Cmd_List ;The parameter list BCS Error ;Optional error handling... ... Cmd_List DFB $04 ;CharRead has four parameters DFB $01 ;Unit number DW $2000 ;Buffer address DW 524 ;Always transfer 524 bytes DFB $00 ;Block (lo) DFB $00 ;Block (med) DFB $00 ;Block (hi) Writing to a Macintosh disk is accomplished with the use of the WRITE command. A call to write block zero to the Macintosh disk in Unit #1 with data at memory location $2000 would look like this: MacWrite JSR Dispatch ;Normal SmartPort Entry point DFB $09 ;Character WRITE command code DW Cmd_List ;The parameter list BCS Error ;Optional error handling... The Cmd_List is the same as in the READ example. Formatting Macintosh Disks The formatting routine in the UniDisk 3.5 firmware can format single- or double-sided disks of variable physical block interleave. The parameters controlling the interleave and the number of disk sides are located in the controller's zero page and are set to defaults whenever the INIT call is issued to SmartPort. These parameters can be altered by using the SET_DOWN_ADR and DOWNLOAD subcalls of the CONTROL call. Once altered, the FORMAT call uses these values in the formatting process. These zero page locations and their values are detailed below: Parameter Location Values Interleave $0062 $02 = Mac, $04 = UniDisk 3.5 DoubleSided $0063 $00 = Single, $80 = Double-sided The following code example formats the media in Unit #1 as a Macintosh disk: MacFormat JSR Dispatch ;Set address to patch interleave DFB $04 ;Control call (Set_Down_Adr) DW Cmd_ListA ;Parameter List BCS Error ; JSR Dispatch ;Now patch the interleave byte DFB $04 ;Control call (DOWNLOAD) DW Cmd_ListB ;Parameter List BCS Error ; JSR Dispatch ;Set address to patch single sided DFB $04 ;Control call (Set_Down_Adr) DW Cmd_ListC ;Parameter List BCS Error ; JSR Dispatch ;Now patch the single sided byte DFB $04 ;Control call (DOWNLOAD) DW Cmd_ListD ;Parameter List BCS Error ; JSR Dispatch ;Finally... DFB $03 ;This is the actual format call DW Cmd_ListE ;Parameter List BCS Error ; RTS The parameter lists are as follows: Cmd_ListA DFB $03 ;All control calls are 3 parms long DFB $01 ;Unit #1 DW Ctrl_ListA ;This has the interleave address DFB $06 ;Set_Down_Adr control code Ctrl_ListA DW $02 ;Two bytes for download address DW $0062 ;Interleave address Cmd_ListB DFB $03 ;All control calls are 3 parms long DFB $01 ;Unit #1 DW Ctrl_ListB ;This has the interleave value DFB $07 ;Download control code Ctrl_ListB DW $01 ;Two bytes for download address DFB $02 ;Mac Disk Interleave value Cmd_ListC DFB $03 ;All control calls are 3 parms long DFB $01 ;Unit #1 DW Ctrl_ListC ;This has the sides byte address DFB $06 ;Set_Down_Adr control code Ctrl_ListC DW $02 ;Two bytes for download address DW $0062 ;Interleave address Cmd_ListD DFB $03 ;All control calls are 3 parms long DFB $01 ;Unit #1 DW Ctrl_ListD ;This has the sides value DFB $07 ;Download control code Ctrl_ListD DW $01 ;Two bytes for download address DFB $00 ;Value for single sided disk Ctrl_ListE DFB $01 ;Format call has just one parameter DFB $01 ;Unit number Note: You may encounter difficulties when switching 400K single- sided disks and 800K double-sided disks in the same drive. STATUS requests for the number of blocks on the disk in the drive are valid for the disk last accessed. Thus, when you READ from an 800K disk, eject it, and insert a 400K disk, a STATUS call will reveal a size of 800K until a READ or WRITE command is issued. Applications which intend to handle both 800K and 400K disks should do a READ before each STATUS call. Further Reference o Apple IIGS Firmware Reference o Apple IIc Technical Reference Manual, Second Edition