Subject: Re: what is a serial BREAK ?
To: Manuel Bouyer <>
From: Jukka Marin <>
List: netbsd-users
Date: 06/02/2005 13:26:40
On Thu, Jun 02, 2005 at 11:51:52AM +0200, Manuel Bouyer wrote:
> What is, from an electrical POW, a BREAK on a serial line ?
> A long period at high voltage level, a long period at the low voltage
> level, or a long period at ground ?

It depends where you look.  At the UART pin, BREAK is a low-level pulse
that lasts as long as or longer than one full character time including
start and stop bits.  In normal 8N1 communication you have one start
bit, 8 data bits, and one stop bit - so BREAK is a low-level condition
lasting 10 or more bit times.

The RS232 drivers and receivers are inverting, so a low level at the
UART output is seen as +12 V on the serial cable.  When the data signal
is idle, it is at -12 V.  (These levels vary - with the drivers used
today, the levels are more like +/- 6 volts or so.)

> I plan to use a MAX232 to convert the TTL signal to RS232 levels,
> and I don't know if I can generate a BREAK by driving the
> MAX232 input, or if I need some extra circuitery.

Yes you can..