[sebhc] Boot ROM modifications

Dwight K. Elvey dwight.elvey at amd.com
Wed Aug 10 11:49:59 CDT 2005

 I think he may be trying to read a 35/40 disk on
a 96tpi drive. I believe that you need to modify
the vector table for the step operation to point to
a double step. This can be done one of several ways.
One is that you can modify the H17 ROM, you can type
in a simple patch from the monitor or, as Barry states,
you can modify the boot sector code to patch the
 It should be simple, you just need to call the code
that does the step twice. It couldn't be more than
about 10 bytes of code. If you are going to patch
it from the monitor, you need to get the table loaded
the first time. I've done this by having the disk
door open and stopping things while the drive is
still spinning. Then you can patch the call table
that the H17 ROM loaded. You should then be able
to pick up the boot operation from where it left
 There may be an issue with the dirve timeouts.
If so, you'll need to start the boot code at the
point that the drive activity is just started but
the tables have already been loaded.
 Explore the H17 listing on from the ftp. You should
be able to patch things to work.

>From: "Barry Watzman" <Watzman at neo.rr.com>
>I don't think that your problem is a function of the boot rom.
>My recollection is that the boot rom only reads in track zero and then
>transfers control to the code contained therein.  All subsequent activity is
>a function of whatever code was on track zero, not of the boot rom.  Track
>zero, of course, can be read identically on either a 40 track or an 80 track
>drive.  Thus, your issue lies in the boot code on the floppy, not in the
>boot code in the ROM.
>[I think]
>-----Original Message-----
>From: sebhc-bounces at sebhc.org [mailto:sebhc-bounces at sebhc.org] On Behalf Of
>West, Ronald S.
>Sent: Wednesday, August 10, 2005 11:59 AM
>To: 'sebhc at sebhc.org'
>Subject: [sebhc] Boot ROM modifications
>Wonder if anyone knows if there was a boot ROM mod to allow the use of a 80
>track drive for booting an H17 disk? I managed to get a TEAC FD-55GFR 193-U
>drive to read a hard sector boot floppy and display the "(BOOT)" prompt on
>my H-8/H-19. It won't go any further in the boot process as it only steps 1
>track instead of 2 needed for the 80 track drive. 
>If someone is interested in how this was done let me know and I will send in
>the details.
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