[Coco] [!! SPAM] Re: [!! SPAM] Re: [!! SPAM] Re: Coco compatible monitors...

[gene heskett]

On Sunday, July 03, 2011 06:57:54 PM jdagget at gate.net did opine:

> Gene
> 
> There is no FPGA that is compatible with the 68pin PLCC socket.
> 
> Besides there are no FPGA's currently in production that is 5 volt
> tolerant. WHile that is not a real issue as one can add FET switches in
> series with the I/O pins and thus be 5 V tolerant.
> 
> The real issue is designing a board that will hold the FPGA and
> ocnfiguration prom as well as the level translators. I have
> investigated this already and there really is no neat solution other
> than a two board approach. The second board could plug into the
> existing PLCC socket or the existing PLCC socket removed and use
> machine pin headers and socket system  like those sold by Samtec.
> 
> What I invisioned was a two board approach where the first board
> contained:
> 
> 1) FPGA - pefered now is XC3S50A in either a 100 pin or 144 pin TQFP.
> The XC3S50A can operate VCCAUX and VCCIO at both the same voltage of
> 3.3 volts. This eliminates the third voltage source.
> 2) Configuration Prom
> 3) surface mounted oscillator.
> 
> The second board will have
> 
> 1) interconnects to the main board as well as interconnects with the
> FPGA board 2) level translators
> 3) dual LDO regulator 3.3VDC as well as 1.2VDC
> 4) resistors for the DAC.
> 
> As for the COCO main board the two crystal pins become free with the
> onboard oscillator module. Also the test pin (#39) could also be
> redefined. WIth those that would allow a Z9 pin to access 2 megs of
> DRAM. Along with any two other functions. One potential would be to
> used for a ram density or refresh rate alteration.
> 
> The two boards could be double sided to keep them both together under
> $20. That is with solder mask and silk screen also. Enlarging the FPGA
> board if room is there, could mean that the memory be moved onto the
> FPGA board and be fast (10nS) SRAM. Though that will definitely
> increase costs considerably. At least $25 more.
> 
> just to let you know that a GIME chip FPGA is doable. Just how and to
> what degree. Furthermore how much is one willing to pay. Also to figure
> out to what level anyone would want to solder and unsolder on their own
> main board.
> 
That does tend to make the cheese a bit more binding, darnit.  But I have 
more than one mainboard, and have not been allergic to a hot soldering iron 
since I was about 7 or 8.  So let me state it this way:  If someone makes 
such a kit, I can write the check as long as obummer doesn't screw that up.

> james
> 
> On 3 Jul 2011 at 9:37, gene heskett wrote:
> > > Hi Gene,
> > > 
> > > One solution maybe to replace the GIME chip with an FPGA. The only
> > > issue though would be to have 5V tolerant I/O as most FPGAs have
> > > 3.3V I/O and 1.8V (?) for the internal core which would require a
> > > few regulators. Gary has a GIME clone in his CoCo3FPGA, so it would
> > > make sense for him to extract that and put it in say a 200Kgate
> > > Spartan 3 if it would fit. I'm not sure if the video I/O from the
> > > GIME chip is multilevel or not. Some video chips have a multi-level
> > > ladder circuit for generating analogue Y-UV output.
> > 
> > The gime's pallette is somehow extracted from a 2 bit d/a on each
> > color, for a 4 level per color lashup.  Now if this FPGA in a Spartan
> > 3 could just drop into the gime socket, I could get interested.  Real
> > interested. Running a 63C09, and a 2 meg disto memory kit, all on an
> > old AT power supply, I have nearly zero heat, the gime is the warmest
> > chip in it, and the power use in that socket could go up to several
> > watts with a suitable heat sink.
> > 
> > I am well aware of the limitations imposed by the coco's OEM power
> > supply and regulator, which could not support that power usage
> > increase without active cooling.  That however is also adjustable, I
> > have done it a couple of times now.  That very inefficient analog
> > design is 90% of the emitted heat in a box stock coco.  It can drive
> > a small 12 volt dc fan from the output of the rectifier, and this is
> > a huge help in maintaining reasonable internal temps.  Whether that
> > additional 150 ma is still within the design envelope of that
> > transformer I don't know, but I have a coco2 and a coco3 equipt with
> > fans, and the coco2 ran 24/7 for 13 years, with 2 drive controller
> > failures.  The lack of a 3 pin power plug on the drive boxes and the
> > coco2 meant that when the studio tower was being used as a lightning
> > rod by mother nature, the resultant EMP surges were pretty hard on
> > the controller.  I eventually married them all together with copper
> > braid, grounded to the rack.


Cheers, gene
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