Lpc2000

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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