Lpc2000

A small word of warning on using this technique... I was involved in a
product that used the maniuplation of the parity mode to fake up the 9th
bit and it worked fine when it was running from a state machine under
interrupt control in DOS but when we went to WIN32 and we had to use the
device driver and had the FIFO on it quickly decended into the pit of
hell. All sorts of timing issues cropped up as you had to be sure that
the character had gone before you changed the parity control bits and
you were never really sure so we inserted delays. This affected the
performance and it also made it very machine specific and we used to end
up endlessly tuning things... Really a Win32 device driver is the only
solution and that was a fairly major project... I don't wish to be a
sayer of doom but do use some caution with this approach especially if
you want to run it on different platforms and machines.

-----Original Message-----
From: Robert Adsett [mailto:subscriptions@...] 
Sent: Wednesday, 16 February 2005 7:02 AM
To: lpc2000@yahoogroups.com
Subject: Re: [lpc2000] UART Interrupt On Bit 9?


At 10:46 PM 2/15/05 +0000, Chris wrote:
>Is it possible to set the LPC21xx uart to interrupt only when a 
>character with bit 9 set (parity=1) is received?  I'm looking at the
>LPC2138 spec, for example, and I don't a way to do this.
>
>Many microcontrollers can do this and the LPC uart is very complete so 
>I thought this may be possible.  Is there a way?

There is a technique I've used on standard PC serial ports ('550 based)
that I would expect to work called parity modulation.  The idea is to
use two 8 bit + parity modes, 8 bit + mark and 8 bit + space.  The
parity bit becomes your 9'th bit.  By interrupting only on a parity
mismatch you get the equivalent of an interrupt on 9'th bit set.  As
with 9 bit mode you can then examine the character received and decide
to go to full reception or continue waiting for the next parity
mismatch.

I have not tried this on an LPC and I don't know if there are any dark
corners in the UART that might give trouble (interactions with the FIFO
might need to be checked).


I hope that's clear.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions, be
they legal, genetic, or physical.  If you don't believe me, try to chew
a radio signal. "

                         Kelvin Throop, III



 
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