Please help me with 16 bit problem

[carl]

I have a 16 bit unsigned long int (as a variable t. so t=16 bit unsigned long int )
and I don't know how I can write this value to two ports.

Using PIC 18f4525
#use fast_io(c)
#use fast_io(d)
set_tris_c(0x00);
set_tris_d(0x00);

Please help

Carl

[meereck]

considering you want to write lower 8 bits to PORT C and upper 8 bits to PORT D:
unsigned int16 value= 0x77FF;
output_C(value & 0xFF); // mask
output_D(value >> 8); // shift left

[carl]

Thanks for replying.

My "value" is a variable called t - (from 0 to 65536)
so i tried your code and changed the value to t:

unsigned long int t;
t= 0x77FF;
output_C(t & 0xFF); // mask
output_D(t >> 8); // shift left

But i have no leds connected to the output to see if 't' is correct.
what should i see??
I have measured voltage with meter but no changes.
Could you also explain the code please - apart from 't' are the hex numbers addresses to write to or actual numbers??

Thanks for your help
Carl
I am using the picdem2 board (v2002)

[meereck]

I have just checked the outcome and it worked for me.
You can also try the following:
unsigned int16 value= 0x77FF;
unsigned int8 tempvar;
tempvar=value & 0xFF;
output_C(tempvar);
tempvar=value >> 8;
output_D(tempvar);

Explanation of the code:
value & 0xFF : since 0xFF means b'11111111', the outcome of the function is that only the lower 8 bits of the value remain.

value >> 8 : shifts value by 8 bits to left so that the lower 8 bits disappear and the upper 8 bits remain. In other words, the upper 8 bits replace the lower 8 bits.

[carl]

Thankyou so much meereck. I will try the code tonight. where does my "t" go though in your code??

Carl

[meereck]

unsigned int16 value= 0x77FF;
that is the variable I put to output ports.

[PCM programmer]

[carl]

So your variable is 0x77FF, My variable is t,

Can i then just put
output_C(t & 0xFF); // mask
output_D(t >> 8); // shift left

or does it have to different

Carl

[meereck]

[carl]

Thanks to all,

I have to go now - although i really don't want to. Please could you just show me how the t is included,

Upmost thanks

Carl

[carl]

First of all thankyou both for all your asistance in this problem. I have been learning as I'm going along.

The code I have tried is:

output_C(t & 0xFF); // mask
output_D(t >> 8); // shift right

(where t is a 16 bit value)


Now because the majority of pins are floating at the moment I am not getting anything out of the ports.Tomorrow i will wire up some LED's (with resistors) from the output pins to pos. Hopefully if t=65536 then all the pins should be high - well thats what i'm hoping.

THanks again for all your help, as well as the links.

Carl

[PCM programmer]

[carl]

OK here is my program so far. It doesn't include all the branches, just the ones that this discussion is on.

Main()
code:

[PCM programmer]

That's not a test program. That's your entire program. A test program
is a small program that tests only the problem area. You said you had
a problem with the output pins floating, even though you had set the TRIS
to "all outputs", and were writing values to the ports.

The program below tests this problem. That's all it does. If it doesn't
work, then you look closely at the program for errors. If you don't see
any, then you look at the .LST file for problems. If it looks OK, then
look at your board for problems. If there's no problem with the board,
then you look at the Errata documentation from Microchip for the PIC.
And so on.

Now, looking at your code below, the first thing I see is that there is no
oscillator fuse. With no fuse, the compiler sets the oscillator config bits
to use the LP oscillator. But that's for a 32.768 KHz watch crystal.
I doubt that it will run a 4 MHz crystal. So the PIC will never start running
and the outputs will remain in the power-up state, which is floating.
Problem solved. Add the XT fuse.

That's why a test program is so important. It's small enough so that
you are forced to concentrate on the problem, and not get lost in
hundreds of lines of code.

[carl]

Ok I understand the posting procedure now. Thanks PCM Programmer, I will do it like this from now on. I will try out several things tonight and hope that it works.

Carl