[Coco] New Coco3 owner

[Gene Heskett]

On Saturday 05 August 2006 00:47, Joel Ewy wrote:
>Mark McDougall wrote:
>> Hi all,
>>
>> Having at one time owned an original silver Coco 1 during its hey-day,
>> I've
>> been a lurker on this group for about 2 years now.
>> ...
>> More recently I've become more interested in the Coco again,
>> particularly since I started my FPGA emulation based on John Kent's
>> CPU09 core. I've even
>> submitted an article which should appear in the next CocoNutz eZine!
>
>    I've been itching to get into FPGA computing as well, but haven't
>managed to save up my pennies yet.  The possibilities are endless.  If
>you had a system with a couple of FPGAs you could implement all kinds of
>hardware and even special purpose processing right there on the chip.
>With a 6809-ish CPU running at 12MHz, plus the capability to do things
>like MP3 or JPEG encoding and decoding in hardware you have the best of
>both worlds -- the simplicity of a CoCo-like system coupled with more
>modern performance.  With modern FPGAs you can (or so I read) change the
>logic functions as fast as you can write SRAM.
>
>> ...o my utter delight I was offered the chance to give a PAL 128K
>> Coco3 a new home - which I picked up yesterday afternoon about 2 hours
>> drive
>> away from where I live. It is in pristine condition and never been
>> opened (until last night). Attached was a Tandy FD-500 disk controller.
>> ...
>> A few questions tho'...
>>
>> It doesn't appear to have an RF connector in the back, despite the
>> existence
>> of the metal can around what would/should be the RF modulator and the
>> channel switch. Should it have one? Has someone pushed too hard and
>> snapped
>> off the connector and pushed it into the can?
>
>    I've never had my hands on a PAL model, but the NTSC CoCo 3 most
>definitely has a connector for the RF modulated output.  On the NTSC
>model it's an RCA jack.
>
Humm, maybe pal models have a scart jack?  Never saw one myself though.

>> What sort of quality should I expect from the composite output?
>> Admittedly,
>> I've become used to seeing the output from MESS and my FPGA board
>> (VGA) but
>> I didn't expect washed-out colours and fuzzy text.
>
>    Composite out on the ones I have is marginal.  Games are generally
>fine.  32- and 40-column text are quite readable.  80-column text is
>pretty blurry.  You can make out the words, but I wouldn't try writing a
>novel without an RGB monitor.  In my experience the colors haven't been
>washed out.  That might be a monitor issue.  Essentially I would use a
>composite monitor or TV for games and similar things, or for programs
>designed for the 32-column screen on the CoCo 1 or 2, but for anything
>involving 80-column text, such as word processing, programming, et
>cetera, I would use an RGB monitor.
>
>> BTW I've since learned that the FD-500 requires a 12V supply and hence
>> requires a multi-pak on the Coco 3.

Which I'm not sure I understand the exact reason that so-called 12 volt 
line was left out of the coco3.  The official reasons was that the power 
supply was approaching meltdown in the coco3.  The rs232 pack derives its 
+-12 volts from an internal switching supply running off the 5 volt line 
obtained from the coco3, and thats a much much heavier load.  It was 
usually made by Aztec, and which I usually disconnect and bypass as mine 
runs in a multipack anyway.  I've also had them go up in smoke!

But, the current draw needed by the 26-3022 from the 12 volt line is 
miniscule, ISTR according to ohms law it's a fraction over 1 milliamp.  So 
it could be restored just for that use with a relatively simple jumper in 
the coco3, getting around 8-9 volts somewhat noisey voltage to the 
26-3022.  If thats not enough, a slight readjustment of the calibration 
pot should bring it into range.

As the current draw is so low, I think rather than grabbing the 8 or 9 
volts from the collector of the 5volt pass transistor, I think I'd add a 
smallish diode right off the transformer, and another filter capacitor, 
maybe 47uf by 16 volts, thereby getting a much cleaner voltage. The ac 
ripple at the collector of the pass transistor can be a couple of volts, 
potentially effecting the 26-3022 even if its readjusted.

>> Anyway, it's quite exciting to have a *real* Coco in my collection
>> now. At
>> some stage I'll look into getting a compatible disk controller (are
>> any 3rd
>> party *floppy* controllers considered "better"?) and also a 6309 and
>> SuperIDE controller (I need to see what all the fuss is about
>> Nitros09)! Would also love to play Nickolas's Donut Dilemma and Pacman
>> Tribute on it too!
>>
>> Regards,
>
>Have fun with it!
>
>JCE

-- 
Cheers, Gene
People having trouble with vz bouncing email to me should add the word
'online' between the 'verizon', and the dot which bypasses vz's
stupid bounce rules.  I do use spamassassin too. :-)
Yahoo.com and AOL/TW attorneys please note, additions to the above
message by Gene Heskett are:
Copyright 2006 by Maurice Eugene Heskett, all rights reserved.