[Coco] Re: [Color Computer] 68881/68882 & the CoCo

[Gene Heskett]

On Monday 06 February 2006 22:07, Mike Pepe wrote:
>I've got a couple of Motorola FPU's in my stash here.
>
>In looking at the manuals, it seems that interfacing the FPU to the
> CoCo is pretty straightforward. It takes 32 addresses, so it would be
> a good candidate for the MPI and switching the whole $FF40-$FF5F SCS
> address range.

In most coco setups, there isn't 32 contiguous addresses free between 
the floppy at $ff40, and the gime table ghost at $FF90+ what with 
floppy controlers with extras, an HD interface, a WP-RS and a dual 
rs232 pack.  With all of the cards installed in my mpi, I think I have 
7 open addresses in that whole range.  I'd suggest an extra decoder 
latch at some open address, 1 byte wide, and 4 other addresses to 
service the 32 bit i/o it would need.  The first two addresses would be 
used to set an address into the chip for the data register to be loaded 
or read.  5 bits of the first latch would be decoded to give the FPU 
its one of 32 address it needs, then the data would be written or read 
by writing or reading the 4 sequential addresses of that 32 bit wide 
register latch, a nice operastion for the 6309 and its ldq/stq 
commands.  And the first latches last 3 bits used to initiate one of 8 
possible operations by the FPU.  Is that enough?  You'd need read/write 
& maybe a start/finish bit, & I don't know what else.

Since the mpi itself uses $FF7F for its front panel, maybe the control 
register could be addressed at $FF7E, and the 4 bytes wide for data 
could then be from $FF78-7B, although I can't recall if mine has 
anything there or not.

Humm, I think I now see what you meant, by using the mpi, the floppy 
controllers $20 wide decoding could be reused.  Humm.  Intrigueing 
thought at that if the SCS signal hasn't been shared and is used by all 
cards plugged in.  I'm not sure mine all meet that spec. 

OTOH, we have a pretty good math and trig library set for os9 programing 
use, so I'm not sure the effort will pay off at the end of the day.  
Fun to do no doubt though, just to prove it can be done.

>Anyone ever do this before? I'm sure it's been done.

Not that I've heard about Mike, but then I'm out here in the hollers of 
WV, so maybe it has been done.

-- 
Cheers, Gene
People having trouble with vz bouncing email to me should add the word
'online' between the 'verizon', and the dot which bypasses vz's
stupid bounce rules.  I do use spamassassin too. :-)
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Copyright 2006 by Maurice Eugene Heskett, all rights reserved.


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