Re: SparcStation 4 serial console

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

> The chip is there and respons on the bus.  Of course, no way to see
> if the output divers of the UART are gone.

One thing I've done on various occasions, which may help if you are
confident enough with electronics to do it: take two LEDs, connect them
in parallel with opposite orientations, and then connect the result in
series with about 200 ohms of resistance.  I use a 100-ohm resistor in
series with each lead, so the resulting thing has two leads of about
equal length, which is mechanically convenient for probing DB25 and DE9
connectors.  As an ascii-graphics approxmation (this is the
two-resistor form),

                +---|>|---+
   ---/\/\/\/---+         +---/\/\/\/---
                +---|<|---+

Then use that between pins 2 and 7, or possibly between pins 3 and 7
(my notes say Suns drive pin 2 and listen on pin 3, but I wouldn't
necessarily trust that, especially when using a cable that might swap
the data pins).  If the pin is being driven one way, one LED should
light; if the other way, the other.  (An idling pin will light one LED
solid and the other not at all.  A data pin with data being sent will
have both LEDs flickering; at the kind of baud rate I'd expect here,
the flickering will be too fast - upwards of a kHz - for most eyes to
detect, so it'll look like dim light from both LEDs.)

For ttyb instead of ttya, either use pins 2 and 7 (or 3 and 7) on your
Y cable's B connector or use pins 14 and 7 (or 16 and 7) on the
machine's connector.

If an output driver is completely dead, you won't get light from either
data pin.  If the driver works one way but not the other, you'll get
flickering from one LED but not the other when data is being sent;
depending on whether it's the mark or the space driver that's dead, an
idle data pin may give you nothing or may give a solid LED.

So long as you don't start connecting up any power sources, you don't
have to worry about shorting things together accidentally; RS-232 is
very nice in that regard.  The requirement on the drivers in the spec
is, IIRC, something like "any pin or combination of pins can be shorted
together, to ground, and/or to any voltage source within range [-20V to
+20V from signal ground, IIRC] indefinitely without damage".

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