Sun 4/330 with faulty serial interface...

[Jules Richardson]

On Mon, 2005-03-28 at 22:41 +0100, John Honniball wrote:
> Jules Richardson wrote:
> > Earlier I cut the A/-B track (which selects which of the two ports on
> > the SCC chip to use) and diverted it via an inverter, so that when the
> > Sun 4/330 thought it was accessing the console port it was actually was
> > using the second serial line - hooked up the physical console to the
> > second port then, but no change in the garbled output.
> 
> No change?  That's odd.
> 
> > So basically that
> > confirms the the SCC chip is broken, and that the parallel - serial
> > conversion is common to both ports on the chip (which is
> > understandable).
> 
> Erm, no the serial/parallel conversion isn't common to both ports
> on the chip. 

Hmm... curious. I'd downloaded the datasheet for the chip and it wasn't
clear either way so figured I'd try the inverter trick. 

> This implies that some buffer chip that feeds to 8530 is
> faulty.

If they are totally seperate channels (no common internal buffering
first, say) then yep, it looks that way. There's no buffers immediately
by the serial logic, so I'll look further afield. 

I've only got the board here with me, not the machine, so can't do any
work under load conditions - but then I'm pretty sure we don't have any
bus extension boards that'd fit this Sun board anyway (it's extremely
deep - much more than I've typically seen on machines with a cardcage)

cheers

Jules