[Coco] Re: Bit 5 of DSKREG

[Brad Grier]

tim lindner wrote:

> Brad Grier <bradgrier at cox.net> wrote:
> 
> 
>>I downloaded the MESS source (I should have done this earlier). There's
>>a comment in cococart.c that bit 5 of the control register at $ff40 not
>>only controls floppy density but is an "NMI enable flag".
> 
> 
> I wrote that.
> 
> I discovered it from my reading of the various schematics for various
> floppy disk controllers.
> 
> I could be wrong, I am not an expert reading schematics.
> 
> Maybe Mark Marlette could chime in to settle this question.
> 

Thanks Tim,

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.

My FDC emulation was so bare bones I'm a little surprised it works as 
well as it does. More work to do...as always.

Brad