[c-nsp] Serial lead

[Christopher.Marget at usc-bt.com]

> > but when connected to a FreeBSD laptop it does send break so it must be a
> > driver limitation
> It's a while since I've looked to be honest, so it's probably my shonky
> memory there. Certainly, I've not found a way using the PL2303 and
> driver that I am (which is a kext file downloaded of them interwebs -
> the driver I had with the device didn't have any OSX drivers on at all)
> using to send break using either Terminal.app or iTerm.
> 
> If anyone is using a driver under OSX, could you let me know what it is?
> Googling didn't seem to bring up anything other than the one I'm already
> using.

PL2303 *can* send a break.  Inability to send break under OSX is a driver limitation (last time I checked, anyway).

There's a terminal emulator that can work around this, however:

Zterm, by dave alverson.

It has a "send break" feature that quickly sets the interface down to 300 (or so) bps, then prints a single NUL character to the port.

"break" is a voltage-high framing error.  High voltage for too long.

Binary zero in RS-232 speak is high voltage.  NUL (zero) is a series of high-voltage intervals.  A series of 300bps high-voltage bits will look like a framing error to a 9600bps Cisco console.

Same result as a break!

You enable the feature within zterm with a shell incantation that updates a zterm configuration file.  The details escape me.