Dragon 64 - test-drb@ccmp.vtda.org

6 Mar 2003

oops!

Guess that was wrong.

I can remember using a Tandy Controller on a Dragon 32
once. But, I guess that one had hacked Coco ROMS.

That might be what I do with this unit, hack a set
Coco ROMS to go into it, just to get it working again.

With a new unit at $35.00, it might not make much
sense to try to get this one working again.

My Coco III is also dead. Green box with no text. I
think the 6809 is bad. At least, that's what I've been
told about these units. So, I'd have to desolder it
and put another one in just to diagnose it.

I may do that some weekend when I feel adventurous.

Suddenly caught the old computer bug....

Al

...
  From: tlindner(a)ix.netcom.com (tim lindner)

  I know I can use a Tandy Controller, but I think
 I'll need a different Disk Basic ROM for it. If
 anyone can help with that, I'd be obliged...  
 Lets see...

 The Tandy controller/software uses the following:

  Read byte, store byte, halt CPU, un-halt CPU,
 repeat. NMI when done.

 The Dragon controller/software uses the following:

  SYNC, interrupt, read byte, store byte, repeat. NMI
 when done.

 On the Tandy controller DSKREG is $FF40, and the
 wd179x is mapped
 between $FF48-$FF51.

 On the Dragon controller DSKREG is $FF48, and the
 wd179x is mapped
 between $FF40-$FF43.

 Also the bit patterns for DSKREG are different
 between the Tandy and
 Dragon controllers:

  *
 ---------------------------------------------------------------
...
   * DSKREG - the control register
  * CoCo ($ff40)                        Dragon
 ($ff48)
  *
  * Bit                                 Bit
  *  7 halt enable flag                  7 not used
  *  6 drive select #3                   6 not used
  *  5 density (0=single, 1=double)      5 NMI enable
 flag
  *    and NMI enable flag
  *  4 write precompensation             4 write
 precompensation
  *  3 drive motor activation            3 single
 density enable
  *  2 drive select #2                   2 drive
 motor activation
  *  1 drive select #1                   1 drive
 select high bit
  *  0 drive select #0                   0 drive
 select low bit

 It would take some serious hacking to transform a
 CoCo FDC into a Dragon
 FDC.

 -- 
 The ears are too length.
 --------------------------------------------------------
...
  tim lindner                   
 tlindner(a)ix.netcom.com 