mikem wrote:
While checking my new Garmin 496 power/data cable, I put a scope on the
NEMA DATAOut line. Just like the EI instruments, the Garmin puts out
TTL (0V and 4V) logic levels instead of the normal RS232 voltage levels
(-5V / -12V to +5V /+12V)

Do all aircraft systems that communicate via "RS232" use the TTL
levels? How about if I drag my Labtop out to the computer to read some
diagnostics or upload a new database?


Is the idle line up or down?

If it's cheated RS-232 (negative half missing),
the idle level is down. If it's logic level,
the idle line (marking) is up.

For a logic-level line you need a MAX232 or clone
to create correct RS-232 levels. For a cheat RS
you need additionally a logci inverter ahead of
the buffer.

HTH

--

Tauno Voipio (OH-PYM, PA28RT201T)
tauno voipio (at) iki fi