18F4550 and TX,RX

[magestik]

Hi,
I have a PIC18F4550 and a RF module.
The RF module has one I/O (transmit, receive), which I connected to both RX and TX of the PIC. Meaning that TX and RX of the PIC are linked together.

I was wondering if it would be a problem, I mean, wouldn't TX bother the RX pin or something ?

For example, if I use fprintf for TX, and not read RX, I think it should be fine,
but if I use fgetc() for RX, wouldn't TX impose a high level ?

Should I use the TRIS function to set TX as an input when I use RX ?

If I'm not clear, please ask for more details.
Thank you.

[Ttelmah]

The problem is not with TX taking the RX line high. This is the required 'idle' level for TTL serial.
There are two problems. The first problem is how is the external module, ever going to take the line _low_, when it receives. The TX line is pulling the line high, when it is not talking. The 'answer' to this, is that you need to add a pull up resistor to the line, and then add the option 'FLOAT_HIGH', to your #use RS232 definition. This tells the compiler to switch the TX _off_ when it is not sending a byte. You need the pull up, since otherwise the line won't actully go high, when it is not being driven.
The second, is that whenever you send a character, you wll also receive this character, so your code will have to read this, and throw it away. How you do this, will depend on the 'nature' of your code. If you are using interrupt driven receive, then the code here will need to be told you are sending, and throw away characters during this time, _or_ be told what characters are being sent, and look for these, and throw them away. If instead your code is basically 'sequential', sending characters, and then waiting for a return, you can write an 'encapsulated' version of putc, which sends one character, and then reads the returned character, before exiting, and use this to send your data.

Best Wishes

[magestik]

Sorry for the late response, just wanted to say that your solution worked like a charm.
Thank you ;).