My retrochallenge entry - Enabling my OSI RAM board

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My retrochallenge entry - Enabling my OSI RAM board

Postby tezza on Fri Jul 04, 2014 10:23 pm

I decided to join this bi-annual even this time.
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Re: My retrochallenge entry - Enabling my OSI RAM board

Postby tezza on Thu Jul 31, 2014 8:20 pm

Bumping this up. My Retrochallenge entry is complete. One month of working on the Ohio Scientific Challenger 4P and blogging as I went, with some good outcomes. It's a great way to focus on things that would normally be in the 'round tuit" corner.
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Re: My retrochallenge entry - Enabling my OSI RAM board

Postby SpidersWeb on Thu Jul 31, 2014 9:19 pm

Wow that's impressive work and a mighty good write up.

I love how you tracked down the jumper settings from an old magazine photo - brilliant.
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Re: My retrochallenge entry - Enabling my OSI RAM board

Postby tezza on Thu Jul 31, 2014 9:26 pm

SpidersWeb wrote:Wow that's impressive work and a mighty good write up.

I love how you tracked down the jumper settings from an old magazine photo - brilliant.

Yes, and the irony being those settings were explained in the OSI book all the time...I hadn't seen it because that section had been left right out of the index! :)

Hidden while in plain sight.
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Re: My retrochallenge entry - Enabling my OSI RAM board

Postby plaing on Mon Aug 04, 2014 4:54 am

Hi Terry,

I just ran across your blog entry on fixing up the C4P for the retrocomputing challenge. Apologies on the red break key thing - I meant to mention that! Anyway - awesome work on the C4P MF. I honestly wasn't too sure what it was - With the drive it seemed like a 4P MF not a 4P...

ANyway it looks like you did AWESOME work on the 4P MF!.

A quick note on one useful 'hack' on the color ram:

Way back in the day I remember realizing that since the scroll command in BASIC only scrolled the video ram and not the color RAM - you could effectively give yourself a reverse video screen - by just writing values to the color ram... I.e. 'Software inverse video'. In those days I didn't have a color display I just used a mono display but it did provide a 'white background with black text'...

It's been too long but something along the lines of:

Code: Select all
5 POKE 56832,5:REM Turn on color?  Did I turn on sound too?
10 V=53248:REM video ram base ($D000 ???)
20 C=V+4096:REM color ram base
30 FOR I=C to C+2047: REM 2K of 4 bits
40 POKE I,240:REM set high nybble to white, low nybble to black
50 NEXT I


I almost certainly have the high nybble value wrong there... I don't have the OSI manuals infront of me - its all from 20+ years old memory...


Anyway - first off so glad to see you got good use of the C4P and it went to a better home than I could have imagined. Nice one on the demo code too - really brought back memories...
Cheers,
Pete
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Re: My retrochallenge entry - Enabling my OSI RAM board

Postby tezza on Mon Aug 04, 2014 7:56 pm

Good to hear from you Pete. I was hoping you would see the blog entry of the C4P work. As you can see I'm putting it to good use :) Thanks for the support.

I don't have to docs in front of me either but I don't think your code is too far from the mark!
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Re: My retrochallenge entry - Enabling my OSI RAM board

Postby plaing on Tue Aug 05, 2014 12:29 am

That was a really impressive set of blog posts too. BTW - I was never sure whether that C2-4P bare-bones was a C2-4P or was from a C2-8P. Not that it matters too much!

What held OSI Back?

I think the *one* other key thing that kept the OSI machines from taking off was the lack of high resolution graphics in the C4P. The character generator graphics are pretty great and fun, but if OSI had made the character-generator ROM switchable to RAM then they could have offerered a programmable character set. Since it uses 2K and 256 characters you have 8 bits worth of addresability so a simple approach to 'medium resolution' graphics would be program it with a 2x4 set which would buy you 128x128... I think there were mods that did something similar to either the 540 or a prior board.

Anyway it's pretty amazing stuff. FWIW on the Color thing - I NEVER saw a C4P on a color monitor at the OSI Users group meetings as a kid - everyone used monitors much of the type you used. I actually used the 'modified' RCA TV on the C1P, you really needed a better monochrome monitor with extra bandwidth to make 64x32 decently readable

I actually really like the 64x32 character resolution. It's tonnes better than 40, 32 or (24 visibile -- C1P/Superboard II) columns.

Pete
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Re: My retrochallenge entry - Enabling my OSI RAM board

Postby tezza on Wed Aug 06, 2014 10:02 pm

plaing wrote:That was a really impressive set of blog posts too. BTW - I was never sure whether that C2-4P bare-bones was a C2-4P or was from a C2-8P. Not that it matters too much!

Yes, I wondered if it was a bare C2-8P too, but I didn't think they ever carried the 502 board. Did they?

plaing wrote:Anyway it's pretty amazing stuff. FWIW on the Color thing - I NEVER saw a C4P on a color monitor at the OSI Users group meetings as a kid - everyone used monitors much of the type you used. I actually used the 'modified' RCA TV on the C1P, you really needed a better monochrome monitor with extra bandwidth to make 64x32 decently readable

Yes, I was really glad I played around with the colour. I imagine a colour machine would have been very expensive at the time, as it needed a colour monitor. It looks like the C4P in question though had an RF board added and wired up to the cassette RCA connector (instead of the cassette). I never verified that but the RF Modulator written on the card is a bit of a giveaway. :D

plaing wrote:I actually really like the 64x32 character resolution. It's tonnes better than 40, 32 or (24 visibile -- C1P/Superboard II) columns.

Agreed!
Tez (Terry Stewart) (Administrator)
Collection: http://www.classic-computers.org.nz/col ... /index.htm
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