#use fast_io, #use standard_io, set_tris_x()

ibg · Joined: 19 Nov 2003 Posts: 22

Hi,

I know I've asking things very similar during the last days but I still don't have the ideas clear about the different methods of doing I/O.

First, I know that every pin must be configured as input or output.

If we are using the directive #use fast_io(port), we are forced to set the direction of the pin using the instruction "set_tris_X()". With such instruction we are accesing to the TRIS_X register that is mapped in memory and we are stting 1's(input) or 0's(output) to the diffrent port pins.

1) Am I right about the stated before?

2) What does exactly mean "using a fast method of doing I/O"?

3) If instead of using "use fast_io(port)", we use "#use standard_io(port)", do we have also to use "set_tris_X()" to specify the pin direction? How do we specify in the standard I/O the pin direction?

Thanks once again 4 your help,

Imanol

Ttelmah · Guest

Humberto · Posted: Fri Jan 16, 2004 6:59 am

Different meanings:

#USE xxxx_IO are PRE-PROCESSOR DIRECTIVES and define HOW the compiler will generate code for input and output instructions.
#USE STANDARD_IO (port)
Cause the compiler to generate code to make an I/O pin either input or output every time it is used. Dont need to set the direction registers but generate extra code for every I/O task.It is the default I/O method for all ports.
#USE FAST_IO (port)
Cause the compiler to perform I/O according to previously direction register settings via set_tris_X().

set_tris_x (value)
Is a COMPILER BUILT IN FUNCTION and allow the I/O port direction (TRI-State) registers to be set.

To see these more clearly just make a small test flashing a LED and take a look at the .lst generated.
Try not using #USE directives nor tris_X() function and you will see that all will run anywise.

hope this help,

Humberto