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      Hello, 
	I'm teaching an RCX-based programming class using the Robolab 
software to a group of 19 4th,5th and 6th graders.  I've been trying to 
get the Robolab software installed and running on the Powermac 5500/225s 
and 6400/200s owned by the school.  Every time I try to run Robolab and 
download firmware or even just test the communication between the 
transmitter and the brick, I get an error saying that the macintosh could 
not communicate to the RCX and the graphical error display shows a red X 
over the transmitter, the cable and the RCX.  However, I do see the little 
green LED inside of the transmitter turning on. I have tried both the 
modem and the printer port but have had no success.  I have tried plugging 
the IR transmitter into the serial port before powering up the machine. 
What's particularly infuriating is that on my G3 at home and various other 
macintoshes where I work, I have no problems with any of the LEGO 
hardware or software. 
	The school's systems administration staff are running an 
access-restriction program called Mac Control from BDW software.  The 
systems staff assures me that that Mac Control will not affect access to 
the serial ports, but I have no way of verifying this short of contacting 
the company (which I am currently trying to do).  The other possible cause 
of the problem may be that the serial ports on these macintoshes are not 
functioning properly.  Does anyone have any experience with these 
particular macintosh models and the availablility (or lack thereof) of 
signals on the DTR and CTS lines? 
	I don't know what version of the MacOS they're running (I'll have 
to check that the next time I'm there), but I see from 
<http://www.ceeo.tufts.edu/troubleshoot/> that I may have problems with 
the L2 Cache Reset.  I'm using the black macintosh serial cable that came 
with the RCX.  I've also tried using a three-piece cable consisting of a 
macintosh serial cable (hardware handshaking--what I use on my modem), a 
DB9-DB25 adaptor and the RCX PC cable.  This hybrid cable has been 
successfully tested on my G3 at least. 
 
	Any advice, words of wisdom or troubleshooting suggestions would 
be greatly appreciated. 
 
Thanks! 
 
--- 
Paul E. Rybski --- http://www.cs.umn.edu/~rybski 
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