There is no easy way to do it, though you can work around it:
You can tell it to generate even, odd, or no parity.  Parity is sent as a ninth
bit, and is based on the number of 1s in the 8 bits of data.  Calculate the
parity yourself, and then change the settings to even or odd so the computer
sets the parity bit according to your needs.

ie:

EVEN parity will set the ninth bit to 1 if there are an even number of 1s in
your 8-bits of data.  ODD parity sets the ninth bit to 1 if there are an odd
number of 1s in your 8-bits of data.
You want to send 01001110 and a 1 as the ninth bit.  This has an even number of
1s.
mscomm.settings = "9600,e,8,1" will make the parity (and thus your ninth bit) 1

If you then want to send 1011100 and a 0 as the ninth bit:
mscomm.settings = "9600,o,8,1" will make the parity (and thus your ninth bit) 1

You should be able to change these settings without closing and opening the
port.  It's extra work, but it should work well for you.

-Adam


Joe McCauley wrote:
>
> Hi,
>
> I need to communicate over tens of meters with several PICs (16f874) using
> RS232. The idea is that all devices listen for their address and then accept
> commands to recieve or send data packets. I am looking for a driver chip to
> allow me to do this. Ideally the driver should be able to recieve data at
> any time, but only turn on its output when data has to be sent by that
> device. (avoiding bus contention)
> Cost is an issue.
> On a slightly OT note, does any one know how to use an MSComm control in
> Visual Basic to send 9 bits of data? I was planning to use the 9 bit mode in
> the PIC to distinguish between address and data.
>
> Thanks for any help
>
> Joe