[plug] Macs and Linux (OLD macs)

[Brad Campbell]

Harry McNally wrote:
> 
> On Fri, 26 Jul 2002 16:15:30 +0800 Brad Campbell <brad at seme.com.au> wrote:
> 
> > I am the LinuxAlien wrote:
> > >
> > > >
> > > >Hell, I had it running on a IIsi with 4 meg of ram.. bit slow in X though
> > > >:p) Even bodged up a serial null modem cable to my laptop to give it a
> > > >network, though ppp at 19,200 baud is a bit painful.
> 
> Could this be tweeked to a faster baud ?

It may do 38400 but you must remember the MAC Serial hardware has no FIFO and with
a slow processor, the kernel has a hard time keeping up with the data.
 
> > > how did you get the serial cable connected, what port?
> > > Tim
> > Printer or modem port.. Just used some nice fine wire and poked it in there.
> > Pinouts are available on the net. The mac uses a varian of rs-422, so you
> > connect the Data + line to ground and connect the Data - line to the Rs-232
> > pin for both tx and rx.
> 
> Oooo. That makes the engineering brain cells cringe. Methinks you may be hurting
> the RS422 driver that way. Actually no. If the parts have overcurrent protection
> it probably hangs in there. Still not nice if the equipment shares a common
> ground because RS232 won't get tidy negative-going swings.

Correct, no negative swings. Practical experience has shown me that most (if not all)
"Modern" rs232 chips will read under about 2 volts as a 0 and not require a negative.
RS232 (EIA-232) drivers are supposed to be limited to 8ma source, and 422(485) drivers
can sink/source 60ma and cope with many volts common mode, so 8-10v from a standard pc
rs252 is not going to do any damage.

-- 
Brad....
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