[Coco] Re: Bit 5 of DSKREG

[Brad Grier]

tim lindner wrote:

> Brad Grier <bradgrier at cox.net> wrote:
> 
> 
>>I also found the source for a Dragon emulator. Like Mess, it checks bit
>>5 to determine whether to enable NMI. It has some specific comments and
>>code for OS9 but I haven't had time to look at it closely.
> 
> 
> The floppy disk controllers are _very_ different for the CoCo and
> Dragon. I did not make this decision based on the Dragon hardware.
> 

The dragon emulator had CoCo 2 support. It also looks at bit 5 when 
deciding whether to enable NMI. It appears you're not alone in your 
decision.

I think that's right because I have a problem with the OS9 boot process 
reading the data register and triggering an NMI at a time when OS9 has, 
for some reason, overwritten the NMI jump at 0x0109. (It later restores 
the vector before NMIs are enabled again).


Brad