[parisc-linux] Re: serial breakout box

collver@linuxfreemail.com collver@linuxfreemail.com
Sat, 9 Feb 2002 09:53:36 -0800

On Mon, Feb 04, 2002 at 10:40:07AM -0800, collver@linuxfreemail.com wrote:
> >>This is an Apollo 400 which has been upgraded to a 715T/50 (Trailways-50). 
> > 
> > Pin 7 is GND.  Pins 2 and 3 are the input and outputs, not necessarily
> > in that order.  Measure from 7 to 2.  Measure from 7 to 3.  One
> > of them will be close to 0V.  The other will be much higher.  I think
> > -10V or something like that.  The pin with the higher voltage is
> > the output.
> > 
> > Do the same thing on the other system also using the 25 pin connector.
> > Then make sure you are not connecting the output to the output.
> It turns out the Apollo 400 has a funky serial pinout.
> I obtained a breakout box and when I find the time, I will experiment with
> this strange serial port.

The Apollo 400 and the mouse are both "DCE".  I can measure -11.44V on the
Apollo's pin 2 and on the PC's pin 3.  I have verified that the mouse will
speak to my PC using only txd, rxd, and rts.  I can also log into the
Apollo from the PC using only txd, rxd, and rts.

It is obvious the I need to connect the mouse's pins 2 and 3, to the
Apollo's pins 3 and 2.  The rest is unsure.  I have tried many combinations
of wiring, and I just haven't been able to get the mouse to work.

To connect two DCE devices, some suggest a "tail circuit cable".  It seems
overkill to me since the mouse only uses a few pins.  I have noticed that
the Apollo doesn't ever show voltage on the "carrier detect" pin.  I have
also noticed that the Apollo voltage is -11.44 volts, and the PC voltage is
-12.15 volts.

Can anyone give me tips for getting this mouse to work?