[Coco] Disto SC (NOT) needed

[Darren A]

On 11/15/08, Joel Ewy wrote:
> Darren A wrote:
>>
>> Roger. The problem is almost certainly a blown HALT line inside the
>> CPU. I've had two such processors which behaved normally except when
>> disk I/O was performed. In both cases, tests revealed a blown HALT
>> line. The 6809 seems to be plagued by this problem. Replacing the CPU
>> will most likely fix the CoCos so they can once again use disks.
>>
>> Darren
>>
>>
> Hmm.  Could you use a Super Controller II with a CPU that has no HALT
> line?  :)  (Probably not easily in practice, since the SCII runs in halt
> mode until the OS-9-only no-halt driver is loaded, and how will you boot
> OS-9?  Can you boot OS-9 over Drivewire?  Or you could burn OS-9 into
> EPROM.  I guess you could also use it in a cassette only system...)
>
> JCE


Even with a standard Tandy controller, it is possible to burn a new
Disk Basic EPROM with a modified version of the DSKCON routine which
does not enable HALT (but still requires that interrupts be masked).
The same could be done for the rb1773 driver for OS-9 and NitrOS-9.
This would allow a CoCo whose CPU has a blown HALT line to be able to
run most disk-based software. Programs which implement their own disk
I/O functions would still be inoperable.

Darren