Sun 4/330 with faulty serial interface...

[John Honniball]

Jules Richardson wrote:
> Just to confirm - Zilog parts labelled Z0853006PSC (SCC) are the same as
> AMD part AM8250H-6 ? (I would think so)

No, the AMD part is an Am8530. The 8250 is something different.

> I've identified whch of the three on the board is responsible for the
> console port (and faulty). However, I've got a Sun "Comm Processor II"
> board in a Sun 3/150 which has eight of the Zilog ICs on board. We don't
> need that many ports for anything, so I'm tempted to do a swap (if I
> don't find a surplus AMD chip in my spares bin). 

I have four Z8530APC chips here, if you want one.

> 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.  If it was, you wouldn't be able to set the two
ports to different baud rates, for example.  The two channels
of the 8530 are completely separate.

This implies that some buffer chip that feeds to 8530 is
faulty.  It may be a 74LS244, and 74LS245 or something similar.
Try to trace bit 6 of the 8530's data bus back to a buffer.

> Time to get the desoldering equipment out I think...

Not so fast!  Check that buffer first!

-- 
John Honniball
coredump at gifford.co.uk