Forums

Disabling UART Receive Interrupt

Started by Richard November 3, 2005
I am working with a RS485 transceiver that echoes the transmitted data
back through the receive channel. When I switch transmission
direction from receive to transmit I wish to ignore the incoming data
as it is just a copy of what is being set. I can't disable the UART1
in the VIC as this would kill all UART operations. So I am trying to
disable the RBR interrupt in the U1IER register. The problem is that
when I do this it triggers an RDA interrupt immediatly.

What am I missing here?

Thanks

Rich


An Engineer's Guide to the LPC2100 Series

Your RS485 level conversion chip, such as an LTC485, should have a
receive enable pin. Tie a line to that and disable reception during
transmit through a GPIO pin.

JP

--- In lpc2000@lpc2..., "Richard" <richas@y...> wrote:
>
> I am working with a RS485 transceiver that echoes the transmitted data
> back through the receive channel. When I switch transmission
> direction from receive to transmit I wish to ignore the incoming data
> as it is just a copy of what is being set. I can't disable the UART1
> in the VIC as this would kill all UART operations. So I am trying to
> disable the RBR interrupt in the U1IER register. The problem is that
> when I do this it triggers an RDA interrupt immediatly.
>
> What am I missing here?
>
> Thanks
>
> Rich
>


jp_thrower wrote:

>Your RS485 level conversion chip, such as an LTC485, should have a
>receive enable pin. Tie a line to that and disable reception during
>transmit through a GPIO pin. >
Yeah. I also use a half-duplex RS485 protocol and I tie the Driver
Enable and Receive Enable pins together on the LTC485. So, when I
activate the driver the reciever is disabled.

TomW >JP
>
>--- In lpc2000@lpc2..., "Richard" <richas@y...> wrote: >>I am working with a RS485 transceiver that echoes the transmitted data
>>back through the receive channel. When I switch transmission
>>direction from receive to transmit I wish to ignore the incoming data
>>as it is just a copy of what is being set. I can't disable the UART1
>>in the VIC as this would kill all UART operations. So I am trying to
>>disable the RBR interrupt in the U1IER register. The problem is that
>>when I do this it triggers an RDA interrupt immediatly.
>>
>>What am I missing here?
>>
>>Thanks
>>
>>Rich
>>
>>
> >
>Yahoo! Groups Links


--
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
----------------


We are using the MAX1480EC fully isolated driver. There is no
receiver enable, only a driver enable.

Rich

--- In lpc2000@lpc2..., Tom Walsh <tom@o...> wrote:
>
> jp_thrower wrote:
>
> >Your RS485 level conversion chip, such as an LTC485, should have a
> >receive enable pin. Tie a line to that and disable reception during
> >transmit through a GPIO pin.
> >
> >
> >
> Yeah. I also use a half-duplex RS485 protocol and I tie the Driver
> Enable and Receive Enable pins together on the LTC485. So, when I
> activate the driver the reciever is disabled.
>
> TomW > >JP
> >
> >--- In lpc2000@lpc2..., "Richard" <richas@y...> wrote:
> >
> >
> >>I am working with a RS485 transceiver that echoes the transmitted data
> >>back through the receive channel. When I switch transmission
> >>direction from receive to transmit I wish to ignore the incoming data
> >>as it is just a copy of what is being set. I can't disable the UART1
> >>in the VIC as this would kill all UART operations. So I am trying to
> >>disable the RBR interrupt in the U1IER register. The problem is that
> >>when I do this it triggers an RDA interrupt immediatly.
> >>
> >>What am I missing here?
> >>
> >>Thanks
> >>
> >>Rich
> >>
> >>
> >>
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >Yahoo! Groups Links
> >
> >
> >
> >
> >
> >
> >
> > --
> Tom Walsh - WN3L - Embedded Systems Consultant
> http://openhardware.net, http://cyberiansoftware.com
> "Windows? No thanks, I have work to do..."
> ----------------
>


Richard wrote:

>We are using the MAX1480EC fully isolated driver. There is no
>receiver enable, only a driver enable. >
Ok, I used that in an 8051 design. I don't get an echo and I don't
disable the UART RX during transmit... TomW

>Rich
>
>--- In lpc2000@lpc2..., Tom Walsh <tom@o...> wrote: >>jp_thrower wrote:
>>
>>
>>
>>>Your RS485 level conversion chip, such as an LTC485, should have a
>>>receive enable pin. Tie a line to that and disable reception during
>>>transmit through a GPIO pin.
>>>
>>>
>>>
>>>
>>>
>>Yeah. I also use a half-duplex RS485 protocol and I tie the Driver
>>Enable and Receive Enable pins together on the LTC485. So, when I
>>activate the driver the reciever is disabled.
>>
>>TomW
>>
>>
>>
>>
>>>JP
>>>
>>>--- In lpc2000@lpc2..., "Richard" <richas@y...> wrote:
>>>
>>>
>>>
>>>
>>>>I am working with a RS485 transceiver that echoes the transmitted data
>>>>back through the receive channel. When I switch transmission
>>>>direction from receive to transmit I wish to ignore the incoming data
>>>>as it is just a copy of what is being set. I can't disable the UART1
>>>>in the VIC as this would kill all UART operations. So I am trying to
>>>>disable the RBR interrupt in the U1IER register. The problem is that
>>>>when I do this it triggers an RDA interrupt immediatly.
>>>>
>>>>What am I missing here?
>>>>
>>>>Thanks
>>>>
>>>>Rich
>>>>
>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>Yahoo! Groups Links
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>--
>>Tom Walsh - WN3L - Embedded Systems Consultant
>>http://openhardware.net, http://cyberiansoftware.com
>>"Windows? No thanks, I have work to do..."
>>----------------
>>
>>
> >
>Yahoo! Groups Links


--
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
----------------


Richard wrote:

>We are using the MAX1480EC fully isolated driver. There is no
>receiver enable, only a driver enable. >
The only way that I see that you could get the MAX1480 to echo the data
transmitted back into the receiver is that you wired the output up in
the Full Duplex mode, and then only used two wires from point-to-point.
e.g. you wired pins 18 + 19 and 17 + 20 together..

You can do that if you are attempting to do collision detection???
However, I have not found collision detection on a 485 network to be of
any value. It is more trouble than it is worth (we used a master-slave
model on the network, not a peer-to-peer).

TomW >Rich
>
>--- In lpc2000@lpc2..., Tom Walsh <tom@o...> wrote: >>jp_thrower wrote:
>>
>>
>>
>>>Your RS485 level conversion chip, such as an LTC485, should have a
>>>receive enable pin. Tie a line to that and disable reception during
>>>transmit through a GPIO pin.
>>>
>>>
>>>
>>>
>>>
>>Yeah. I also use a half-duplex RS485 protocol and I tie the Driver
>>Enable and Receive Enable pins together on the LTC485. So, when I
>>activate the driver the reciever is disabled.
>>
>>TomW
>>
>>
>>
>>
>>>JP
>>>
>>>--- In lpc2000@lpc2..., "Richard" <richas@y...> wrote:
>>>
>>>
>>>
>>>
>>>>I am working with a RS485 transceiver that echoes the transmitted data
>>>>back through the receive channel. When I switch transmission
>>>>direction from receive to transmit I wish to ignore the incoming data
>>>>as it is just a copy of what is being set. I can't disable the UART1
>>>>in the VIC as this would kill all UART operations. So I am trying to
>>>>disable the RBR interrupt in the U1IER register. The problem is that
>>>>when I do this it triggers an RDA interrupt immediatly.
>>>>
>>>>What am I missing here?
>>>>
>>>>Thanks
>>>>
>>>>Rich
>>>>
>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>Yahoo! Groups Links
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>--
>>Tom Walsh - WN3L - Embedded Systems Consultant
>>http://openhardware.net, http://cyberiansoftware.com
>>"Windows? No thanks, I have work to do..."
>>----------------
>>
>>
> >
>Yahoo! Groups Links


--
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
----------------