Re: 9 bit communication on RS 232

[EMAIL PROTECTED] (Chris Giese) wrote in message news:<[EMAIL PROTECTED]>...
> [EMAIL PROTECTED] (suchitra) wrote:
> 
> >Hello All
> >I wanted to know how can we configure com port for 9 bit
> >communication.
> >I intend to use the 9th bit as Address/data bit..since i want to
> >communicate with more than one devices.
> 
> Set up the serial chip to use "stick parity". This is described
> in the serial chip documents. The parity bit is "stuck-at-0"
> or "stuck-at-1" while the other 8 bits are being transmitted.
> 
> You can't change the parity bit until transmit is complete.
> However, the Transmitter Empty (TEMT) bit in the serial chip
> does not generate an interrupt. This means that transmit
> must be polled, which may not work (or not work _well_) under
> Windows. Turn the FIFO off too; if the serial chip has one.
> 
> The receive side of the software must detect and interpret
> parity "errors" to recover the 9th bit.

As noted by others, if stick parity is availiable (win32 API supports
it) use this, otherwise the only option you have is to fiddle parity
between odd and even on a byte-by-byte basis (I once got this going on
Sun Solaris for Intel and guess that linux would be much the same)

There are one or two manufacturers of ISA/PCI serial comms. cards that
support 9-bit mode, try

http://www.mv.com/ipusers/effsol/products.html