[Coco] COCO3 System Arrangement of modules

[Gene Heskett]

On Friday 23 May 2008, John T Chasteen wrote:
>Hello COCO Family
>
>I would like to get your opinions about a COCO3 System arrangement
>COCO3 with 6309 connected to an Upgraded MPI unit
>Place the Floppy in slot #4, Cloud9 SuperIDE unit with
>a Cloud9 configured CF unit and CFA (CF Adapter).
>
John, I think you may be walking in pretty high grass there.  I could be wrong, 
but I think the boot device is hard coded to be in slot 4, although a rebuild 
of nitros9 after changing that code might be possible.  I think, subject to 
corrections, that the CF must therefore be used as an attachment to the floppy 
controller in slot 4, else the code that manipulates the slot selector in the 
mpi will switch you away from the CF access you want.

Also, and here is a download saver, please open up the mpi and jumper all 4 
sockets so pin 8 is common to all, else os-9 will probably miss any irq's 
generated by incoming data from an i/o card in one of the other slots.

Doing this will also commonize the 4 irq pullup resistors located near the front 
edge of the mpi board, 3 of which should be removed as they represent enough of 
a load that some cards may not have enough stuff to pull the irq line down, or 
may blow the transistor doing it.  If that transistor is part of a larger 
integrated circuit, ooops.

Those resistors are labeled r1, r2, r3 & r4 on one mpi I have, but can be 
identified by an ohmmeter connected to the socket's pin 8, and probing them, 
you should find 4 virtual short ( < 2 ohms ) circuits on one end of each of the 
correct resistors, remove 3 of them.

By enabling the bypassing of the unselected slot's irq, so it gets to the coco 
regardless, the os itself will look for the source of the irq, manipulating the 
slot access until it finds the guilty card and will service the interrupt with 
no more than a 150 microsecond lag, more likely 15 to 20 microseconds though, 
the 150 is absolute worst case I ever measured, and fast enough you'll never 
miss an incoming character from the rs-232 pack again.

>I want save files from my Cassette tapes.
>Save files from 5.25 floppy disk.
>Transfer files to the CF or the CFA units
>Use the CF to boot.
>
>I would like to also use my Drive Wire cable to
>download files (disk images or files) from the internet
>or from my _PC hard drive.
>
>Do you see any bugs in this conciliation

Just the caveats I pointed out, John.  Boisy, Robert, Mark or Alan may correct 
me, but that's how I've understood it for about 15 years. :)

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
"There is nothing new under the sun, but there are lots of old things 
 we don't know yet."
 -Ambrose Bierce