[ On Sat, March 29, 1997 at 22:16:18 (GMT), der Mouse wrote: ]
> Subject: Sun-3/260 serial ports
>
> ohmmeter shows zero resistance between the terminal's pin 7 and the
> ground pin on its power cord.  IMO this is severely broken of the
> terminal; circuit reference ground should not be earthed

Yes indeed!  (but not uncommon in simpler equipment, I've found).

>   But of course the Sun is also broken - pin _1_ could
> reasonably be earthed, but connecting my circuit's reference point to
> pin 1 does nothing, and the diagram in the -3/260 book shows no
> connection for pin 1.)

This is also quite common.  As you probably also know there should
always be only one connection from the shield to earth, at one and only
one end.  I'd normally put this at the computer end, and indeed Sun may
be assuming the physical shell is grounded.

All of the books that I have which discuss RS-232 say that the frame
ground (or protective ground) (FG, pin 1), is often left unconnected.

> This is so totally bizarre I just have to ask, is it just that this
> particular board is fried, or do other people see similar brokenness?

examination of my spare 3/260 CPU shows no visible connection through
all the layers to pin one on either serial port, nor do I measure any
connection to any other obvious ground reference (either logic or frame)

-- 
							Greg A. Woods

+1 416 443-1734			VE3TCP			robohack!woods
Planix, Inc. <woods@planix.com>; Secrets of the Weird <woods@weird.com>