AVR-Chat

On Wed, Dec 14, 2005 at 06:02:05PM -0000, Don Kinzer wrote:
> --- In AVR-Chat@yahoogroups.com, Bruce Parham <obparham@j...> wrote:
> > ... switching thresholds at +/- 6v.
> 
> I have been able to send serial data to many different PCs using TTL 
> outputs (mark=0V, space=+5V, nominally).  No problems yet.

Ditto.

The problem I have run across is sometimes even a premium brand PC
doesn't bother to provide negative voltage on the so-called no-longer
RS-232 ports. The result was about 0.25 volts for logic true, 3 volts
for logic false (RS-232 is inverted). Laptops are particularly bad about
this.

0/+3 happens to work on classic 1488/1489 buffers, "but its not right."

Super serious workstations used to rigidly ahere to +-10 volts. Many put
pullup or pulldown resistors on handshake inputs to set their desired
state if the line was not connected as some ancient UARTs would flat out
not run unless all the handshake lines were correct.

Have never seen the switching thresholds raised to 6 volts as some
have stated.

-- 
David Kelly N4HHE, dkelly@HiWAAY.net
========================================================================
Whom computers would destroy, they must first drive mad.