How Do I Use Printf to Send Text to a Peripheral?

The printf() function does two things:

1.Formats text based on the format string and placeholders you specify.
2.Sends (prints) this formatted text to a destination (or stream).

See printf Function and The Printf Routine for more information.

The printf() function performs all the formatting; then calls a helper function called putch(), to send each byte of the formatted text. By customizing the putch() function you can have printf() send data to any peripheral or location. You can choose the printf() output go to an LCD, SPI module, or USART for example.

A stub for the putch() function can be found in the compiler’s pic/sources directory. Copy it into your project, then modify it to send the single byte parameter passed to it to the required destination. Before you can use printf(), peripherals that you use will need to be initialized in the usual way. Here is an example of putch() for a USART on a mid-range PIC device.

void putch(char data) {
  while( ! TXIF)  // check buffer
    continue;     // wait till ready
  TXREG = data;   // send data
}

You can get printf() to send to one of several destinations by using a global variable to indicate your choice. Have the putch() function send the byte to one of several destinations based on the contents of this variable.