[Coco] deluxe rs232 pak / MPI

[Gene Heskett]

On Tuesday 24 November 2009, Aaron Wolfe wrote:
>Hi,
>
>I just acquired an rs232 pak and MPI.  The MPI seems to work fine with
>my coco 3, at least my drivewire rom pak works fine through it.
>I haven't been able to get the rs232 pak to work in basic or nitros9,
>with or without the MPI.  I have the original documentation from
>tandy, was wondering if things have changed for use in the coco 3.
>Also I have the 6309 instead of 6809, maybe this has some effect.  The
>MPI is 26-3024 "updated for use with the coco3".
>
>the docs say to do "EXEC &HC000" or "EXEC 49152" to access the setup
>routine in the pak's rom.  This results in various lockups on my coco
>3.
>
The slot switch must be to the slot the pack is in at powerup unless the MPI 
has been jumpered.  If it has been jumpered, then the packs eprom should be 
pulled as there are other packs you may have plugged in that will also have 
that as an exec address.

>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.

>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.

>saw some posts about that.
>any tests I can do in basic, with the rs232 pak directly connected?  I
>
>saw a post about peeking values, they said:
>> ?PEEK(65384) usually reports 0 initially
>> ?PEEK(65385) usually reports 16 initially
>> ?PEEK(65386) and ?PEEK(65387) should report 0 initially
>
>the answer in the thread was that the user doing the troubleshooting got:
>
>
>?PEEK(65384) 0
>?PEEK(65385) 112
>?PEEK(65386) 0
>?PEEK(65387) 0
>
>I also get exactly these results, if that means anything.
>
>Basically I am not sure if the rs232 pak works, it was in storage for
>many years.  I am completely new to using an rs232 pak or an MPI, and
>actually new to OS-9 as well, so there are a huge number of unknowns
>here.  any hints or recommended practices are much appreciated. I'm
>not sure what tests to do to start eliminating possibilities.

There is a possibility that the Aztec inverter supply in the pack has gone to 
that great retirement pasture.  Since you have the MPI, you have the plus and 
minus 12 volt supplies the chips need available in the mpi.  You have to 
remove the Aztec assembly, and wire the cards edge connector to feed those 
voltages in where the Aztec was feeding them.  ISTR I had to superglue a 
couple of strips of thin copper plate into the blank spaces to do that.  
PITA, but it works for me, and has been for at least a decade.

That rewired pack will NOT work in a coco3, as the coco3 has no -12 volt line 
at all, and the load on the +12 line may be the straw that writes fini to the 
coco3's power transformer if its not actively cooled.

>-Aaron
>
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>


-- 
Cheers, Gene
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