[Coco] Coco compatible monitors...

[John Kent]

On 3/07/2011 12:43 AM, gene heskett wrote:
>
> I think that is the general idea Roy's device uses, along with a couple of
> pots to scale the a/d response to the machine.  It is quite usable, with
> some reservations about the blue because the tendency to set the pots to
> reduce the digital background noise also takes away some of the gain, and
> since the blue is the least amplitude, it suffers.  I think this may be a
> characteristic of my gime also, and if some way to enhance the gimes rise
> and fall times could be found, that would alleviate much of the problem.
>
> Unforch, the output stages in the gime were apparently on a power budget.
> Mine has rise&  fall times in the 400ns range.  Since the cm8 was also
> severely limited, so severely that trading it for a Maggy 515 was a huge
> improvement, but even that never made a blue 80 column text screen
> readable.
>
> I have no clue if raising the VCC on the gime would help, never tried it,
> basically because if you push the envelope and blow the gime, there aren't
> any replacements other than raiding another coco3. It might be amazing what
> 6 volts on the VCC pin might do for it.
>
> I have even considered sampling the memory signals and making my own set of
> 2 bit d/a's to replace the gime's anemic output stages, but I need to make
> some round tuits first as I have people clamoring for them.  Still looking
> for suitable artwork for (preferably 2 difference faces so there is a heads
> and a tails sides) that.  What I have found on the net is either way too
> complex to try to put on a 50 cent sized coin due to the carving time
> involved (a whole page of text), or best described as ugly.  Graphics files
> for something attractive gratefully accepted.
> Cheers, gene
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.

Round tuits ? I have plenty of uncompleted projects too.

John.

-- 
http://www.johnkent.com.au
http://members.optusnet.com.au/jekent