#use rs232 & printf mystery

[bdeb]

Hi gurus,

Been tinkering with the RS485 examples
and.. ehh.. have a question because it works??


(Examples includes 2 serial comms, one with terminal/PC and one with
other units on RS485 multidrop network)

Comm with PC is set up in main file with "#use rs232(... stream=PC)"

After that "RS485.c" is included which defines similar "#use rs232(... stream=RS485)"


So far so good.

Rx/Tx via RS485 is done using "fputc(xx, RS485)" as expected,
but when sending prompts to the PC, a normal "printf()" is used!
(i.e. NO "fprintf(PC, ...)" as I´m using)


The only way I see how this can work, is that you rely on the compiler to put the "#use rs232(...)" from the included
file BEFORE the same command in main file.
(According to doc´s, "printf()" uses the latest "use-statement" for it´s output.)

Am I right or have I missed something crucial here??


By the way, RS485 is working excellent - much thanks to all 9 pages of topics posted here on the subject..


Regards:


/Björn
PCM 4.112 on 16F690

[Humberto]

The "#use rs232(...)" directives for each comm must include the assigned Tx/Rx pins AND the STREAM parameter
to redirect the printf output.

Defining:
#use rs232 (baud=9600,xmit=PIN_C6,rcv=PIN_C7,enable=PIN_C5,stream=RS485)
it doesn't matter if it is in an included file

In the header of your main.C
#use rs232 (baud=9600,xmit=PIN_B1,rcv=PIN_B0,stream=PC)

To transmit to the network:
fputc('A', RS485);
To transmit to the PC:
fprintf(PC, "Tx to PC");

Regards.

[bdeb]

Hi Humberto,

I totally agree! My question was why it still works if you *don´t* do like that.

Pins are of course declared in real "#use-statements" - not included
in my text for two reasons;

They are not the issue + I don´t know how strict policy is about
not posting code from examples.

Thanks!


/Björn

[Ttelmah]

Printf, or putc, always send their output to the _last_ RS232 definition.
So if you declare the RS485 stream first, you can do a putc/printf, without using the stream commands, and talk to the other stream.

Best Wishes

[bdeb]

Hi Ttelmah,

OK, I assume you agree with my theory on why this example works.

Sorry for asking about these finnicky details, but since I use
the MPLAB IDE, I have to put all my driver code in .h files which make
things a bit messy and also depending on the compilers good will.
(Linker only working if you use CCS IDE, right?)

Checking the list file is OK, but understanding is better..


Thanks!


/Björn