[time-nuts] TTL to RS-232

Hal Murray hmurray at megapathdsl.net
Tue Feb 13 21:24:15 EST 2007


> This cable had a DB 9 on one side and the other plugged in to the cell
>   phone. From his suggestion, I cut off the cell phone plug end and
> stripped the   wires. Plugged it in to a pc with procomm running in
> "chat" mode. It was just a   process of elimination to see which one
> was sending data and which received   data. Hooked it directly to the
> GPS engine and it worked. A TTL to RS232  adapter  for less than $4. 

Neat.  Thanks.

Is there a silicon chip in the DB-9?  Maybe powered off the modem control 
signals.  You can check with an ohm meter.

There are two issues with "TTL" signals on GPS units.  One is the voltage 
swing.  The other is an inversion.  The standard MAX232 type chips also 
include an inverter.

Some GPS units don't need an inverter.  They have TTL (actually 5V CMOS) 
levels.  That's good enough for most RS-232 receivers but I wouldn't try it 
on long/noisy lines.  If you add a MAX232, the inversion will break things.



-- 
These are my opinions, not necessarily my employer's.  I hate spam.






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