[Coco] deluxe rs232 pak / MPI

[Gene Heskett]

On Tuesday 24 November 2009, Aaron Wolfe wrote:
>On Tue, Nov 24, 2009 at 9:09 PM, Gene Heskett <gene.heskett at verizon.net> 
wrote:

[...]

>>>hmm.  I can't get the EXEC to work even when the rs232 pak is directly
>>>connected to the CoCo, no MPI.  Could this mean a bad rs232 pak?
>>
>> Good question.  Unforch I don't have a pat answer. I believe someone else
>> answered with an exec &HE010 to put it back in the rom only mode first.
>
>yes, this allowed me to access the rom's setup program.. somehow I
>missed those answers before.

So you are actually running the code in the rs232 packs rom then.  I've not 
looked at that more than 2 or 3 times ever.

>>>I think I have to have the MPI's switch set to the slot my drivewire
>>>rompak is in so that the HDB DOS rom loads.
>>>Does this mean I cannot use the rs232 pak as the same time, or maybe
>>>this just means I must wire the IRQ lines together?
>>>
>>>>>looking through the nitros9 source I see that FF68 is base address for
>>>>>T2, and FF6C for T3.  Tried both with basically the same results.  I
>>>>>see there is a compiler flag for MPI usage, it is set.  I am not able
>>>>>to try nitros9 without the MPI because currently I must boot from
>>>>>drivewire  (really looking forward to that SD card pak, if you're
>>>>>listening Roger :).  the rs232 pak does not appear to have been opened
>>>>>for any modifications, label covering the screw was intact until I
>>>>>opened it just now to look for obvious bad components.
>>>>>
>>>>>when I "iniz /t2" or /t3, sometimes I get error 246, sometimes it
>>>>>works.  when it works, an irq routine shows up in the "irqs" command
>>>>>and the device is listed in "devs".  however, all attempts to pass
>>>>>data do not seem to work.  sometimes the coco locks up about the same
>>>>>time data is sent into the port, so I assume this means something
>>>>>somewhere is working, sort of?  might just be coincidence to be
>>>>>honest.
>>>>>
>>>>>should I put the rs232 pak in a specific slot of the MPI?
>>>>
>>>> I believe that most folks put it in the front slot, aka slot 1, byte
>>>> $FF7F=00.
>>>
>>>is there a setting in NitrOS-9 to tell it to set FF7F to 00?  Would
>>>this break the drivewire rompak in another slot?  (this rom is how I
>>>am booting nitros9)
>>
>> Nitros9 normally maintains $FF7F at $33 in order to access the floppy
>> controller in the back slot.  The convention for IRQ service routines is
>> to read it, save it, and set it for the slot that this IRQ service
>> routine is preset to access its hardware at.  And when the IRQ has been
>> serviced, put the saved value back into $FF7F.
>
>The driver must assume slot 1 for the rs232 pak and manage $FF7F
>correctly, as it is working fine there now while running off the
>drivewire for disks.  I'll have to take a closer look at the driver to
>figure out how/where it's doing this.

I believe that is the case, although both the address and the slot can be 
"adjusted" with the more recent versions of os9's xmode utility.

>>>>>do i need to wire all of the interrupt lines in the MPI together to
>>>>>make this work?
>>>>
>>>> Mine has been so wired for about 22 years, excellent idea if for no
>>>> other reason than all IRQ's _do_ get through to the cpu.  In your case,
>>>> it sounds like the IRQ from data rx'd may have gotten through, but the
>>>> slot switch, or the logic at $FF7F, is preventing the IRQ service
>>>> routine from accessing the pack, which in turn clears the IRQ, so you
>>>> effectively have an IRQ stuck on.
>>
>> And I forgot that doing so also parallels all the pullup resistors, one
>> for each slots pin 8, presenting the device attempting to pull down the
>> IRQ line with perhaps more current to sink than it can do comfortably.
>>  There are 4 resistors along the front edge of the pcb in the MPI that
>> are all alike, and may be as low as 2700 ohms each, I've seen 4700's and
>> 2700's there.  It is safe to break out 3 of them, there by reducing the
>> current the IRQ asserting transistor has to sink to do its job.
>
>sounds tricky for a software guy like me..  my soldering will make you
>laugh (or cry).

Probably cry, since I've had a hot soldering iron in my hand for a living for 
a little over 60 years now.  That, FWIW is why I said break them. :)

>> If the aztec supply is pulled, then it can never be used in the coco3,
>> only in the mpi.
>
>ok makes sense.  I think I'm lucky to avoid this issue for now.
>thanks for all the advice!

NP, glad I was of some assistance.

-- 
Cheers, Gene
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