[Coco] MC6883 x 74LS785

Daniel Campos daniel.campus at gmail.com
Sat Sep 10 12:17:48 EDT 2016

Thanks to everyone that privately sent me the 74LS785 datasheet. I have 
done some more tests and discovered that the CoCo2B board only 
recognizes 32Kb of RAM when using a MC6883. If I replace it with a 
74LS785 it works just fine and recognizes the full 64K RAM.

- Also tested replacing the 2x 4464 DRAMs for 8x 4164 DRAMs (the board 
has the places for both), but the result is the same.
- For those who asked, yes, I tested all the 3 MC6883 used in the tests 
and they work just fine on another CoCo2 (not 2B) that I have here.
- I have tried to replace the CB 1.3 + ECB 1.1 EPROM from another with 
the CB 1.2 + ECB 1.1, but with no effect.


Em 10/09/2016 04:40, Simon Jonassen escreveu:
> Here you go
> http://roust-it.dk/coco/SN74LS785N.pdf
> /Simon :-)
> -----Oprindelig meddelelse-----
> Fra: Coco [mailto:coco-bounces at maltedmedia.com] På vegne af Daniel Campos
> Sendt: 9. september 2016 21:50
> Til: CoCoList for Color Computer Enthusiasts
> Emne: [Coco] MC6883 x 74LS785
> I just received this week a CoCo2B, but instead of have a 74LS785 SAM, it
> have an old 6883. The result is an erratic memory behavior with NitrOS-9
> crashing when loading, etc.
> Anyone has any documentation or datasheet about this newer SAM ? I have
> done a quick search on google but found nothing relevant.
> Daniel

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