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Serial Communication w/ AT89C51 or AT89C52

I want to have a simple program to print something out using hyperterminal. Also it would be nice to receive a character and echo it back. I have been able to do this in assembly but I can't get it to work in C. Here is the latest code I have tried:

#include <AT89X51.H> 
#include <CTYPE.H>
#include <STDIO.H>

int i;

void main()
{
SCON = 0x50; //SCON: mode 1, 8-bit UART, enable rcvr
TMOD = 0x20; //TMOD: timer 1, mode 2, 8-bit reload 
TH1 = 0xFD; //TH1: reload value for 9600 baud @ 11.0592MHz 
TR1 = 1; //TR1: timer 1 run 
TI = 1; //TI: set TI to send first char of UART 

while (1) 
{
P1 ^= 0x01; 
printf ("\n\nHello World\n\n"); 
i = _getkey();
putchar('$');
putchar(i); 
}
}

Is there anything wrong with my code? Or is there something in how I am compiling? I am confident my hardware is fine because I can get it to work in assembly. Any help would be appreciated. Thank you.

Parents
  • ... something:

    of course include these Declarations:

    extern char putchar (char c);
    extern char _getkey ();
    

    either via a header file or directly into your c-File.

    I'm also not sure about the underscore-Character in
    _getkey:

    The name of a function (i.e. it's assembly-label),
    that passes values via Registers is prefixed by an
    underscore character.

    _putchar is correct, but I guess
    _getkey must be labelled __getkey
    with two underscores:
    one for the name and
    one for the non void-void-signature property.

    If I remember well, then - let
    T
    be a
    non-void type specifier -
    T function (void);
    must also be labelled
    _function:

    I'm at home now, so I cannot look it up in the manual.

    Norbert

Reply
  • ... something:

    of course include these Declarations:

    extern char putchar (char c);
    extern char _getkey ();
    

    either via a header file or directly into your c-File.

    I'm also not sure about the underscore-Character in
    _getkey:

    The name of a function (i.e. it's assembly-label),
    that passes values via Registers is prefixed by an
    underscore character.

    _putchar is correct, but I guess
    _getkey must be labelled __getkey
    with two underscores:
    one for the name and
    one for the non void-void-signature property.

    If I remember well, then - let
    T
    be a
    non-void type specifier -
    T function (void);
    must also be labelled
    _function:

    I'm at home now, so I cannot look it up in the manual.

    Norbert

Children
  • I included <stdio.h> in my code. I found the declarations in that header file. Will this take care of that problem. Also do I need to add the header files I use to my source group or another group on the left of the window? Thanks for the help.
    Jake

  • "...do I need to add the header files..."

    No, you don't need to add them.
    However, you might find it useful to add them; eg, to give quick access to open a frequently-used header. In that case, you'd need to clear the 'Include in Build' option - otherwise uVision will try to separately compile your header(s)!!

  • stdio.h will do.

    You can understand the #include - control as a substitute of
    pasting the Text of the included File into the including module.

    The preprocessor of C doesn't anything else.

    If you costumize the functions, you must add your
    custom object file(s) to the list of objects to be linked.

    You're maybe talking about the "left window" of your IDE.
    I don't use an IDE for 8051 Projects. I just hack the text into
    files, using a text editor. Then invoke compiler and linker directly
    via Windows-Explorer and entries in the Registry:

    [HKEY_CLASSES_ROOT\c_auto_file\shell\C51-Compiler_Emulator\command]
    @="C:\\C51\\BIN\\C51.EXE  %1 DEFINE ( TEST_CODE = 1 ) OE PP"
    

    Norbert