Lpc2000

Insert sound of hand slapping forehead.  Thank you.


Richard

--- In lpc2000@yahoogroups.com, Peter Jakacki <peterjak@t...> wrote:
> Ok, I was going to take a stab at this and say it looks like you 
might 
> just need to bias your 485 line to make sure it sees an idle 
condition 
> when there is nothing driving the line. A quick look at the 
datasheet 
> reveals it's covered for open circuit conditions. But the early 
485 
> chips would tristate the receive (uart) line when they were 
disabled. 
> It's hard to find that in most documentation but it is in the TI 
doco, 
> right there on page 11 where it shows the function tables.
> 
> So, when your rx is disabled your uart rx line is floating. 
Solution? 
> Just add a pullup of course.
> 
> Hope it's that simple.
> 
> Peter
> 
> 
> 
> 
> Richard wrote:
> 
> >
> >I have tried to disable the UART1 interrupt both in the UART 
itself 
> >and in the VIC.  The problem is that as soon as the interrupts ar 
re-
> >enabled it is triggered.
> >When the 485 driver is set the read the bus the RX pin of the 
2104 
> >is brought low this, I believe, is detected as a start condition 
and 
> >is the first false interrupt.  
> >When the driver is set to read the RX line is brought high.  I 
> >believe this is detected as a stop condition and presents a false 
> >00H as having been received.
> >
> >Richard
> >
> 
> 
> 
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