Lpc2000

Peter Homann wrote:
> Hi,
> 
> I am migrating a serial communications interface (Modbus) to a LPC2138 
> processor. The Modbus spec defines that an end of message has occurred 
> when a period equal to 3.5 characters has passed since the last 
> character has been received.
> 
> The LPC uart can generate an interrupt if the receive buffer has 
> characters in it and no character has been received for a period of 3.5 
> - 4.5 characters.
> 
> I would like to use this feature for detecting the end of a received 
> message. The problem I have is that if I service an interrupt due the 
> the buffer being filled, and it also happens that that last character in 
> the buffer was the last character for the received message, the receive 
> time-out interrupt will not occur, resulting in the end of message not 
> being detected.
> 
> Is there a solution, other than using a buffer length of 1 and using a 
> timer to measure the inter message gap?
> 
> Cheers,
> 
> Peter.
> 

Hello Peter,

this interrupt was not designed for your needs. It should prevent a
communication from being stalled if some characters are trapped in queue
which is not full.
Just an idea: every time you receive a character reset a timer. If a
timer interrupt occure prior a line idle interrupt, you have not
received any characters for a certain time. It's ugly but should solve
your problem.

  Sten

-- 
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