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using uart1 without tx

 
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hansknec



Joined: 30 Sep 2004
Posts: 25
Location: Virginia, USA

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using uart1 without tx
PostPosted: Mon Jun 16, 2008 8:52 pm     Reply with quote
PIC18F1320.
PCWHD version 4.071.

I am using the hardware uart for serial receive, but I am not doing any transmitting. I use an interrupt (INT_RDA) to capture the incoming serial, so I have to stick with the hardware uart.

I am using the #use rs232(baud=9600,uart1) preprocessor command and my receives work perfectly, but it takes over the TX pin RB1 and holds it high. Is there anything I can do to release it? I have tried setting the TXSTA byte to zero, but then I lose receive as well for some unknown reason.

Running very low on pins, so I sure would like to get RB1 released for I/O.

Thanks.
Ttelmah
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PostPosted: Tue Jun 17, 2008 2:13 am     Reply with quote
Define both pins as normal for the hardware UART, as you are doing.
Then add:
Code:

#byte TXSTA=0xFAC
#bit TXEN=TXSTA.5

#define UART_TX_OFF TXEN=FALSE
#define UART_TX_ON TXEN=TRUE

You can then have:

UART_TX_OFF;

in your code, and just the transmit part of the UART gets turned off.
Now, you _may_ have problems with TRIS. I always use 'fast_io', and this then works fine, if I set the corresponding TRIS bit and '0' for output, or '1' for input. However the compiler will still think the bit is used fo the UART, and if left to using 'standard_io', may well keep trying to set the TRIS bit to '1' (which is what is needed for UART operation).
Two ways round this, either switch to using fast_io, or access this pin, and it's TRIS directly, using bit definitions.
It takes a little bit of fiddling, but does work fine (has been posted here a few times in the past).

Best Wishes
hansknec



Joined: 30 Sep 2004
Posts: 25
Location: Virginia, USA

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PostPosted: Tue Jun 17, 2008 6:56 am     Reply with quote
Thanks Ttelmah,

That's a relief since I already had 50 boards made using the TX pin to drive a fet.

I know it was probably posted before, but I seem to have difficulties getting the search engine to give me a meaningful list from my search requests. Too bad we can't put a google search engine in it. It would eliminate a lot of stupid duplicate requests (like the one I just asked).
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