[Coco] 6820 and 6821 pin compatible?

[Mike Pepe]

That could very well be the case. I don't think I even have 6820 datasheets in my library!

The 6822 is indeed electrically different, but in most CoCo cases if you blow up a 22 a 21 will work just fine in its place as the 22's are pretty hard to come by. Best source I know of is dead CoCo 1's :)

> -----Original Message-----
> From: coco-bounces at maltedmedia.com [mailto:coco-
> bounces at maltedmedia.com] On Behalf Of jdaggett at gate.net
> Sent: Friday, November 06, 2009 11:47 AM
> To: CoCoList for Color Computer Enthusiasts
> Subject: Re: [Coco] 6820 and 6821 pin compatible?
> 
> On 5 Nov 2009 at 20:53, Mike Pepe wrote:
> 
> > Should work just fine. As I recall the major difference between the
> two was the 6820 had dynamic registers while the 6821 was static. But
> I'm sure if I'm wrong someone will chime in.
> >
> 
> 
> Mike
> 
> You maybe right, though I seem to remember something about the port
> sink and source
> currents were not very strong and the part blew port pins. Though I
> could be wrong as this
> recollection dates back now almost 30 yrs. I think the MC6820 was
> discontinued in very early
> 80's.
> 
> I do know that the MC6822 differed in that the ports were open drain
> and would work with
> voltages upwards to 15VDC.
> 
> james
> 
> 
> 
> > > -----Original Message-----
> > > From: coco-bounces at maltedmedia.com [mailto:coco-
> > > bounces at maltedmedia.com] On Behalf Of Joel Ewy
> > > Sent: Thursday, November 05, 2009 7:34 PM
> > > To: CoCoList for Color Computer Enthusiasts
> > > Subject: [Coco] 6820 and 6821 pin compatible?
> > >
> > > I'm restoring an SWTPC 6809 computer.  I intend to run OS-9 on it.
> I
> > > also want to try out FLEX and UNIFLEX (the latter of which I'm sure
> > > this
> > > computer once ran).
> > >
> > > I've got a timer board, that I believe (judging from the OS-9
> > > configuration of the SWTPC emulator) provides the system clock
> > > interrupts.  It has a socket that, according to the documentation,
> once
> > > housed a 6820, but now sits empty.  I can probably dig up the
> > > documentation, but I bet somebody on this list can tell me without
> > > cracking a book or downloading a PDF whether or not I can just plop
> a
> > > much more readily available 6821 in there instead.
> > >
> > > If you're interested in following my progress on this project, I've
> > > been
> > > blogging about it:
> http://8littlebits.wordpress.com/category/swtpc/
> > >
> > > The CoCo gets mentioned as well, and I used a CoCo emulator to make
> a
> > > boot disk image I'll eventually use when I'm ready to try and boot
> this
> > > thing up.
> > >
> > > JCE
> > >
> > >
> > > --
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> > > Coco at maltedmedia.com
> > > http://five.pairlist.net/mailman/listinfo/coco
> >
> >
> > --
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> 
> 
> 
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