Re: Serial ports/Cables/IIGS

[Roger Johnstone <roger@ihug.invalid>]

In <C5NAb.24169$dr1.4020175@news4.srv.hcvlny.cv.net> John Smith wrote:
> I have been using a null modem adapter to connect to my PC just fine.  
> Works perfectly.  I recently purchased a Magellan Meridian GPS, which 
> has a serial connection on it.  I am able to connect to it through 
> Hyperterminal, but I'm unable to connect to it with the //gs.   The 
> GPS only has tx, rx, and gnd in a DB9 plug.  I have a normal hardware 
> handshaking modem cable for my //gs. Is this a cabling problem?  I 
> tried my printer cables and they didn't work either.  Am I missing 
> some setting or something?

Most GPS equipment uses an NMEA serial interface. NMEA uses 0 volt/5 
volt levels instead of the -12V/+12V that RS-232 uses. I have seen 
adapter cables which use a MAX232 TTL-to-RS232 level converter chip 
inside them. On a PC at least one of the handshaking lines rests at a 
high level when it's not being used, which of course is the case when 
the port is set to software or no handshaking. This is used to power the 
converter chip.

If this is the case with your cable you may need to connect power to the 
handshaking pins on the DE9 plug.

-- 
Roger Johnstone, Invercargill, New Zealand

PS/2 Mouse Adapter for vintage Apple II or Mac
order at http://vintageware.orcon.net.nz