🚀 go-pugleaf

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In response to numerous requests, I am posting some info on drive density
switching:

To change density, you must call SIO, after setting up the IOCB as follows:

Device=$31   (D)
Unit= Drive #
Command= $4E (N) to READ CONFIG
       = $4F (O) to WRITE CONFIG

Byte Count = 12
Aux Bytes= (not normally used, but some DOS's use as part of formatting)

Also a "P" command is supported by some drives (like INDUS) to reconfigure
on demand prior to formatting.

The bytes transferred are:

byte 0: Tracks per side (40 std)
     1: Drive step rate (west. dig. std....0 fast 3 slow)
     2: zero (hi-byte of sectors/trk)
     3: sectors per track (18 for std...26 for 1050 mode)
     4: number of sides (0=single 1=double)
     5:  disk type: 
         bit 2: (0=single den, 1=double den)
         bit 1: (0=5-1/4"      1=8 ")
     6: hi-byte bytes/sector  (0 for 810 compat)
     7: lo-byte bytes/sector  (128 for 810   256 for double den std)
     8: translation byte:
         bit 7: (1=40 trk on 80 trk drive)
         bit 6: always 1 ...indicates drive present
         bit 1: 1= make boot sectors (1-3) full size
         bit 0: 1=sectors numbered 0-17 not 1-18
     9-11: undefined

These bytes are transferred TO the progran on a read config, modifications
may be made, and a WRITE CONFIG will change the desired options.

The comment about it not working on an 810 is specious....Obviously
these commands will only work on configurable drives...like PERCOM, INDUS,
ATR8000 controller, etc.

On more note; thos using MYDOS are prompted for these options when using
menu selection P from DOS...It internally generates the CONFIG command
and executes it. I have placed a BASIC program to configure drives on
some ATARI bulletin boards, but I'd have to look for a copy now...
It's been several years since I wrote it!

	Rob Botwin, N2FC
    .....{utah-cs|seismo|decvax}!harpo!eagle!houxm!mtuxo!mtuxn!rb
	ATT/IS Labs (201) 577-5016 (Cornet 8-270-5016)
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